# Why you should keep the N249.......



## Dave926 (Mar 30, 2005)

http://www.audizine.com/forum/showthread.php/554859-N249-delete-Why-you-should-not-do-it

Discuss.......


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## AmIdYfReAk (Nov 8, 2006)

I do get minor surge with my stage 2 setup once i installed the SSQV, but that was due to the firm spring and the lack of "push" from the stock 5psi, 8psi was enough for it to vent. 

I didn't notice ANY adverse effects from my n249 delete at all, but then again there is a world of difference between the audi 1.8's and the jetta 1.8ts in terms of hardware and software differences.


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## taverncustoms (Feb 18, 2011)

this is only relative to stock style DV's. if you run a Synapse DV the N249 is useless.


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## Dave926 (Mar 30, 2005)

taverncustoms said:


> this is only relative to stock style DV's. if you run a Synapse DV the N249 is useless.


I dont believe whatever style dv or bov has to do with how fast an intake manifold builds vacuum, that was the point of this thread.

Point is, there is a reason why vw used this, and then went to even faster operating electric dvs on fsi cars.


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## kg6dxn (May 4, 2012)

My n249 has been removed and my ECU tuned by 034. I have none of the jerky issues described in the other thread. The n249 also requires a vacuum vessel to perform the job off idle. At part throttle I can hear my DV partially open as the boost spools up and it closes. 034 pulled out all the n249 stuff when they did my dyno tune. This may be the real difference. Many of us just download a tune and go. I had 034 work on my car for 3 weeks on/off to dial it it perfectly. My goal was not max HP, it was max driveability with as much HP the could squeeze out.

I think the bottom line is in the tune. If the ECU is setup to run without the n249, the car will run fine. Mine does. My 034 tune also uses the n75 to control boost. This gives me a smooth flat boost plot on the log to 20psi. My car is doing around 325hp at the crank. I have no boost spikes. I have no turbo surge. I have no turbo lag. I have no problems.

If you built 20 engines all the same, each one will run slightly different. Each will have their own quirks. Maybe some of us need the n249 to run correctly? I don't.


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## Sim (Jun 27, 2002)

I do not agree with the OPs statement in the other thread. N249 and the DV is there for regulating the boost level in the charge pipe, therefore it needs the extra vacuum reservoir (to be able to open, even under positive manifold pressures). As you may or may not know, the boost is NOT the same before and after TB in part throttle applications where our small (original) turbos can deliver a lot more air than the engine can breathe (with partially opened TB). N249 is there to prevent developing too much pressure difference (causing jerkyness). If the tune(r) is aware of the removed solenoid, may modify the part throttle N75 duty cycles so no excessive overpressure can build up in the charge piping.

I have found N249 removal to open the DV faster(!), them probem with the (slight) compressor surging are usually caused by the stiff springs in the BOVs. They have to be stiff(!) otherwise the BOV could open in the situation described above (higher pressure pushing it up from below than going in on the top via the nipple).


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## Twopnt016v (Jul 5, 2009)

I call BS. My car loved it when I removed the n249. I don't want a stinking valve messing with my boost pressure yo! lol:wave:


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## Dave926 (Mar 30, 2005)

kg6dxn said:


> My n249 has been removed and my ECU tuned by 034. I have none of the jerky issues described in the other thread. The n249 also requires a vacuum vessel to perform the job off idle. At part throttle I can hear my DV partially open as the boost spools up and it closes. 034 pulled out all the n249 stuff when they did my dyno tune. This may be the real difference. Many of us just download a tune and go. I had 034 work on my car for 3 weeks on/off to dial it it perfectly. My goal was not max HP, it was max driveability with as much HP the could squeeze out.
> 
> I think the bottom line is in the tune. If the ECU is setup to run without the n249, the car will run fine. Mine does. My 034 tune also uses the n75 to control boost. This gives me a smooth flat boost plot on the log to 20psi. My car is doing around 325hp at the crank. I have no boost spikes. I have no turbo surge. I have no turbo lag. I have no problems.
> 
> If you built 20 engines all the same, each one will run slightly different. Each will have their own quirks. Maybe some of us need the n249 to run correctly? I don't.


If it took 034 3 weeks to tune a car, I would have questioned that first.

Second, the turbo surge isnt something you will see on a gauge, simple as that. Its there in a data log. In regards to lag, its not going to make a difference with that. The difference will be with re-spool during shifts.



Sim said:


> I do not agree with the OPs statement in the other thread. N249 and the DV is there for regulating the boost level in the charge pipe, therefore it needs the extra vacuum reservoir (to be able to open, even under positive manifold pressures). As you may or may not know, the boost is NOT the same before and after TB in part throttle applications where our small (original) turbos can deliver a lot more air than the engine can breathe (with partially opened TB). N249 is there to prevent developing too much pressure difference (causing jerkyness). If the tune(r) is aware of the removed solenoid, may modify the part throttle N75 duty cycles so no excessive overpressure can build up in the charge piping.
> 
> I have found N249 removal to open the DV faster(!), them probem with the (slight) compressor surging are usually caused by the stiff springs in the BOVs. They have to be stiff(!) otherwise the BOV could open in the situation described above (higher pressure pushing it up from below than going in on the top via the nipple).


Sim,

The n249/dv does not control the boost pressure in the charge pipe. The extra vaccum stored in that resevoir is there for when you let off the throttle, to open the dv/bov faster.

Having the tuner lower duty cycles isnt going to do ****. Wastegates on a stock turbo start at 5psi, and the vast majority of us here arent using stock turbos. Duty cycle can be 0%, the turbo is still going to build boost.




Twopnt016v said:


> I call BS. My car loved it when I removed the n249. I don't want a stinking valve messing with my boost pressure yo! lol:wave:


Unless someone can provide data proving faster respool and no compressor surge, going by seat of the pants feel for something that happens in less than 0.5s is going to be wrong.

There is a reason a group of Bosch engineers decided this was a better thing to do, and I can for sure say its not emission reasons.


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## Sim (Jun 27, 2002)

Dave926,

My opinion is diffetent than yours, but that is not problem . N249 and the DV is (!) helping in the boost regulation, it is opening/closing fast to try to reduce the boost level (in the case it would be too high). And this is a fact, thats why it has the reservoir. The DV/BOV does not need additional vacuum to get opened, as the throttle body closes, there will be instant vacuum for the DV/BOV to open. The N249 just introduces a restriction in the control hose, therefore it may be advantageous to remove it. But thats only my sole opinion.


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## Twopnt016v (Jul 5, 2009)

Dave926 said:


> Unless someone can provide data proving faster respool and no compressor surge, going by seat of the pants feel for something that happens in less than 0.5s is going to be wrong.
> 
> There is a reason a group of Bosch engineers decided this was a better thing to do, and I can for sure say its not emission reasons.


I don't really need to provide data, I'm giving my personal experience. My car had a part throttle surging issue and you could hear the DV being actuated when I did not want it to. I tried a different n249 and it made no difference. I removed the n249 and the car stopped doing that. The DV will work faster when it has a direct vac source to the intake manifold and doesn't go thru the n249/vac canister. Have you tried the mod and had bad luck? Have you never tried the mod and ran across the article and decided to post it to deter others from doing the mod? I'm confused Either way I had good luck with it. We all know that what translates better on paper or what engineers had in mind doesn't always play out the best in the field.:beer:


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## Sim (Jun 27, 2002)

Dave926 said:


> Having the tuner lower duty cycles isnt going to do ****. Wastegates on a stock turbo start at 5psi, and the vast majority of us here arent using stock turbos. Duty cycle can be 0%, the turbo is still going to build


Believe me, on a small turbo you can easily end up with 8-10 psi higher boost in the charge pipe than in the engine itself. This may cause quite ****ty part throttle feel (not mentioning your 5psi wastegate to open/close until boost finally settles). Of course, there is no need to finetune the part throttle n75 duty cycles, it just distinguishes a good tune from a bad one.


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## kg6dxn (May 4, 2012)

Dave926 said:


> If it took 034 3 weeks to tune a car, I would have questioned that first.
> 
> Second, the turbo surge isnt something you will see on a gauge, simple as that. Its there in a data log. In regards to lag, its not going to make a difference with that. The difference will be with re-spool during shifts.


034 took 3 week because I was squeezing service in right before SEMA. They finished after SEMA. The dyno tuning only took 8 hours but included new coil packs, spark plugs, MAF housing and a tune up.

I saw the data logs during my dyno session. Almost perfectly flat. With my setup, it works fine without the n249. I have a 4" exhaust, no CAT, no EGR, mo SAI, no smog. I can get 20psi at 2500rpm is I want it. No re-spool issues.

Like I said before, it comes down to the tune. In my case, it runs and performs fine without an n249.

There's nothing wrong with you running one. If your car runs better with it, keep it.


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## turbo2.24.1990 (Jun 2, 2008)

I'd keep the n249. The only evidence I saw from the other side supporting that the n249 isn't completely necessary is that that the turbo's are capable of handling a brief spike in pressure at throttle shut. Obviously there are limits to this though. Bottom line is a quicker dv reaction is better-not saying that it can't be sorted out pretty well with the correct hardware, but that the n249 makes a good case for quicker dv reaction. The mkv electronic dv is a dead giveaway for proof of this in my eyes. As far as light load situations, it's hard to see a reason why a bypass around the turbo and intercooler wouldnt be good idea for efficiency. I believe some people were having a legitimate problem with the system intact, but most people deleted just because they were told to. Regardless, I think the system is great if the time is taken to get it operating properly.


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## elRey (May 15, 2001)

I used to be in the N249 del camp. Then I went thru the trouble of adding it to my car. From now on, I'll suggest using it on any ME7 build in the future.

Is it night and day? No. But it addresses enough of the rough edges to be worth it. <- Subjective


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## luchos (Feb 23, 2012)

Sim said:


> I do not agree with the OPs statement in the other thread. N249 and the DV is there for regulating the boost level in the charge pipe, therefore it needs the extra vacuum reservoir (to be able to open, even under positive manifold pressures). As you may or may not know, the boost is NOT the same before and after TB in part throttle applications where our small (original) turbos can deliver a lot more air than the engine can breathe (with partially opened TB). N249 is there to prevent developing too much pressure difference (causing jerkyness). If the tune(r) is aware of the removed solenoid, may modify the part throttle N75 duty cycles so no excessive overpressure can build up in the charge piping.
> 
> I have found N249 removal to open the DV faster(!), them probem with the (slight) compressor surging are usually caused by the stiff springs in the BOVs. They have to be stiff(!) otherwise the BOV could open in the situation described above (higher pressure pushing it up from below than going in on the top via the nipple).


I believe you are correct sir:beer:


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## turbo2.24.1990 (Jun 2, 2008)

luchos said:


> I believe you are correct sir


If both of you believe that the DV is what regulates boost pressure, what the heck do you need the wg or n75 for-why don't you delete those too? Weld that wg shut, delete the n75 and plug the DV in there. The wg and n75 are the only things that regulate the boost being created by the turbo. They control the pressure in the charge pipes. The DV is only there to bleed off the boost that's been created when the boost isn't required anymore. 



Twopnt016v said:


> My car had a part throttle surging issue and you could hear the DV being actuated when I did not want it to. I tried a different n249 and it made no difference. I removed the n249 and the car stopped doing that.


 What kind of DV where you running when you had the part throttle surging issues?-im assuming aftermarket. Perhaps the n249 system doesn't respond well to aftermarket DVs with different spring rates. Just a thought, but do you think the delete worked for you because the intake manifold is capable of developing a higher vacuum than the vacuum reservoir is capable of holding? I think it's critical to match the DV's needs to the vacuum source capability-perhaps that was what was happening?


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## Sim (Jun 27, 2002)

turbo2.24.1990 said:


> If both of you believe that the DV is what regulates boost pressure, what the heck do you need the wg or n75 for-why don't you delete those too? Weld that wg shut, delete the n75 and plug the DV in there. The wg and n75 are the only things that regulate the boost being created by the turbo. They control the pressure in the charge pipes. The DV is only there to bleed off the boost that's been created when the boost isn't required anymore.


That is what you think (along with most of the other), but it is not correct. I am writing this last time: N249 is originally there to assist boost regulation (limitation). If E CU thinks boost is too high, it will use the DV to bleed off excessive air to potect the engine! This is not the subject of an argument, that is a fact and i am actually disappointed (shocked) to see people NOT KNOWING ME7 spreading around BS.

I have got high speed MAF voltage logs proving that there is absolutely no compressor surge for my k03 using the original DV with no n249.


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## luchos (Feb 23, 2012)

Sim said:


> That is what you think (along with most of the other), but it is not correct. I am writing this last time: DV is originally there to assist boost regulation (limitation). If E CU thinks boost is too high, it will use the DV to bleed off excessive air to potect the engine! This is not the subject of an argument, that is a fact and i am actually disappointed (shocked) to see people NOT KNOWING ME7 spreading around BS.
> 
> I have got high speed MAF voltage logs proving that there is absolutely no compressor surge for my k03 using the original DV with no n249.


This is absolutely correct, if all the dv valve did was dump the excess boost after you lay off the throttle, there would be no need for the secondary vacuum reservoir. The n249 reservoir is there for when you are under boost to open the dv valve momentarily to prevent over-boosting.


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## Sim (Jun 27, 2002)

Thank You Luchos! 

EDIT: Of course DV is there also to bleed off air when the throttle plate is closed and that is its primary task. I guess that was not a question .


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## Dave926 (Mar 30, 2005)

Sim said:


> That is what you think (along with most of the other), but it is not correct. I am writing this last time: N249 is originally there to assist boost regulation (limitation). If E CU thinks boost is too high, it will use the DV to bleed off excessive air to potect the engine! This is not the subject of an argument, that is a fact and i am actually disappointed (shocked) to see people NOT KNOWING ME7 spreading around BS.
> 
> I have got high speed MAF voltage logs proving that there is absolutely no compressor surge for my k03 using the original DV with no n249.


Please tell me how a MAF signal is going to spike, during a shift, from compressor surge?


Also, if a manifold build vacuum fast enough, please tell me why the FSI cars use an electric dv?


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## Twopnt016v (Jul 5, 2009)

turbo2.24.1990 said:


> What kind of DV where you running when you had the part throttle surging issues?-im assuming aftermarket. Perhaps the n249 system doesn't respond well to aftermarket DVs with different spring rates. Just a thought, but do you think the delete worked for you because the intake manifold is capable of developing a higher vacuum than the vacuum reservoir is capable of holding? I think it's critical to match the DV's needs to the vacuum source capability-perhaps that was what was happening?


When I purchased the car used it had stock DV and had the issue. I swapped a know good stock unit and still had issue. I pulled an APR R1 valve off another car and it still did the same thing. I bypassed the n249( after trying a new n249) and the problem went completely away. The n249 was being sent a signal by the ecu to bleed off boost and the valve would actuate the DV while on part throttle causing surging. I agree the DV needs to have a proper vac source and there is not one better than straight off the intake manifold. Right now I am running the MadMax DV in push orientation meaning the DV is flipped around from how it is stock so boost pressure and a solid vac source are opening the valve vs just having a vac supply to actuate it. No part throttle issues, no boost leaks, super quick DV actuation with lighting fast recovery speed.


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## Sim (Jun 27, 2002)

Dave926 said:


> Please tell me how a MAF signal is going to spike, during a shift, from compressor surge?


No, I wasnt talking about MAF signal spiking, i meant that removing N249 will not hurt the turbo by making the DV (or BOV) to open too slowly and causing compressor surge. If it does open slow, then it is (probably) because the spring is too stiff or due to other mechanical malfunction. "Sadly" these cars with small turbos (which can generate lots of boost (in the charge pipe) even on part throttle) need the stiff springs!

Compressor surge can be detected by logging the MAF output voltage (not the translated and filtered g/s reading)!

Here is an example of a bad, non opening DV (with failed diaphragm). Air is rapidly oscillating in the turbo air inlet pipe back and forth after letting off throttle (compressor surge).









Here is an example of a good DV. All OK.









Here is an example of a BOV (HKS SSQV) with slight fluttering.









BTW: I ran the bad DV for almost two years with no damage on the turbo (stock boost). The car with the fluttering SSQV runs a TFSI turbo on 1.2bar for more than 6 years now.



Dave926 said:


> Also, if a manifold build vacuum fast enough, please tell me why the FSI cars use an electric dv?


System integration, cost reduction (no need for extra solenoid "n249", vacuum canister, check valve, vac piping, air return piping, mounting hardware and at last but not least no need for the DV either). An integrated electric DV makes it possible to bleed off boost (on full throttle) a lot more easily than as they did it on the 1.8t (with all the crap).


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## Dave926 (Mar 30, 2005)

First and second log dont show the big pressure spike after letting off the throttle, thats the point of this thread, or at least the point I am try to emphasize here.

The last log shows it clear as day, coming off the the throttle is a large pressure spike right after. N249 would cure that, and woukd also result in a faster respool as well.

Any chance you could post a log of that last car, during a full throttle run?


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## Sim (Jun 27, 2002)

To be the honest, i do not see any pressure spike on the last one.

Here is one of the same car with a spike! Now got me!  The spike is not more than ~0.25 bar (~3-4 psi).









If that spike hurts a turbo, then it wont last long anyways. Also i am sure the spike would be there with the N249, too.
That car has been abused (http://www.youtube.com/watch?v=8aq7Z9TwIAk) i can tell you, but the turbo is still intact!


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## elRey (May 15, 2001)

N249 helps smooth things out when driver changes loads e.g. letting off a little 90% pedal to 80% pedal. The car responses faster to driver's request with the aid of the N249. The car will feel like it's more connected to the pedal. This may be more pronounced on a big turbo b/c of the inertia of the large wheel/shaft.

For me that was reason enough to add it. I didn't and still don't think it affects turbo life enough to worry about it. Tho I do have many, many logs before/after showing how it eliminated the spike at throttle plate closing.

I will add that ME7 tries to predict pressure spikes/over shooting associated with driver letting off pedal (even a little) and then tries to prevent 'expected' over shoot. BUT it's *specifically* tied to decreasing pedal angle, not boost regulation like stated earlier. Tho I guess it could be considered a function of boost regulation.


There's also respool after shifts. Humor me, let's assume there is a small spike @ throttle close during a gear change without N249 and not (or smaller) with N249. Which situation do you think will have a higher turbo shaft speed when throttle is opened again? Again, this is more applicable to big turbos.


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## Sim (Jun 27, 2002)

elRey said:


> N249 helps smooth things out when driver changes loads e.g. letting off a little 90% pedal to 80% pedal. The car responses faster to driver's request with the aid of the N249.


There is hardly any difference between 80% and 90% TPS. Absolutely no need to do anything with the DV. Also please refer to one of my first posts in this topic about N249 regulating boost level in the charge pipe. You have just wrote the same.



> There's also respool after shifts. Humor me, let's assume there is a small spike @ throttle close during a gear change without N249 and not (or smaller) with N249. Which situation do you think will have a higher turbo shaft speed when throttle is opened again? Again, this is more applicable to big turbos.


1. Do not use a BOV, use a DV.
2. Do not close TP at all, use ALS (or flat shift).

You do not need any more faster respool which could not be achieved by these. If you do not like (accept) turbo lag, go and get a NA car.


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## elRey (May 15, 2001)

Sim said:


> There is hardly any difference between 80% and 90% TPS. Absolutely no need to do anything with the DV.


Depends on the car. And that was an example. Please feel free to swap in an acceptable pedal gradient.



Sim said:


> Also please refer to one of my first posts in this topic about N249 regulating boost level in the charge pipe. You have just wrote the same.


But with MORE insight.



Sim said:


> 1. Do not use a BOV, use a DV.
> 2. Do not close TP at all, use ALS (or flat shift).
> 
> You do not need any more faster respool which could not be achieved by these. If you do not like (accept) turbo lag, go and get a NA car.


1. **scratch head**
2. So, this thread only applies to ALS equipped cars? Sorry, I missed that.

You side-stepped the question.

edit: Ah, you did answer my question: From your last statement you imply N259 allows a faster shaft speed during shifts. Thanks.


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## turbo2.24.1990 (Jun 2, 2008)

Sim said:


> N249 and the DV is there for regulating the boost level in the charge pipe





Sim said:


> EDIT: Of course DV is there also to bleed off air when the throttle plate is closed and that is its primary task.


This is the point I was referring to, N249 and DV are not there to regulate boost. The WG and n75 are there to control boost pressures, that is their primary function. The N249 and DV's primary function is to bleed off the pressure that's being created/ manipulated by the turbo, WG, and n75. The byproduct of the N249 and DV's primary function-which is to bleed the boost off as quickly and efficiently as possible-is that it "regulates" the pressure in the charge pipes.


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## Sim (Jun 27, 2002)

elRey said:


> But with MORE insight.


I dont think so. I will not write it down again, that N249 can bleed off boost under wot if ECU wants to. You say it is only bleeding when throttle angle is decreasing. Thats not MORE insight, that is a different story.



> 1. **scratch head**


Sorry, cant help if you do not know what is the difference between a BOV and a DV.



> 2. So, this thread only applies to ALS equipped cars? Sorry, I missed that.
> 
> You side-stepped the question.


Of course not. But if any one wants a super fast respool, (i suppose he or she is racing at that moment) ALS is a good solution. Or you need super fast respool when cruising with 10% TPS?! Dont make me laugh.

BTW: Fast respool is definitely not achieved by introducing a ca 1.5-2mm restriction in the BOV/DV control line!!!


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## Sim (Jun 27, 2002)

turbo2.24.1990 said:


> This is the point I was referring to, N249 and DV are not there to regulate boost. The WG and n75 are there to control boost pressures, that is their primary function. The N249 and DV's primary function is to bleed off the pressure that's being created/ manipulated by the turbo, WG, and n75. The byproduct of the N249 and DV's primary function-which is to bleed the boost off as quickly and efficiently as possible-is that it "regulates" the pressure in the charge pipes.


I gave up!


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## elRey (May 15, 2001)

Sim said:


> N249 and the DV is there for regulating the boost level in the charge pipe, ....
> N249 is there to prevent developing too much pressure difference (causing jerkyness).





Sim said:


> N249 and the DV is (!) helping in the boost regulation, it is opening/closing fast to try to reduce the boost level (in the case it would be too high). And this is a fact, thats why it has the reservoir. The DV/BOV does not need additional vacuum to get opened, as the throttle body closes, there will be instant vacuum for the DV/BOV to open. The N249 just introduces a restriction in the control hose, therefore it may be advantageous to remove it. But thats only my sole opinion.





Sim said:


> That is what you think (along with most of the other), but it is not correct. I am writing this last time: N249 is originally there to assist boost regulation (limitation). If E CU thinks boost is too high, it will use the DV to bleed off excessive air to potect the engine! This is not the subject of an argument, that is a fact and i am actually *disappointed (shocked) to see people NOT KNOWING ME7 spreading around BS*.





Sim said:


> Of course DV is there also to bleed off air when the throttle plate is closed and that is its primary task. I guess that was not a question .



Before I call you out, let me see if I understand you correctly....

Are you saying that IF there is not a negative gradient in pedal (pedal angle decreasing) i.e. pedal angle doesn't change/or increases/stays WOT, and Actual boost is greater than Requested boost, that ME7 will open DV?


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## Sim (Jun 27, 2002)

elRey said:


> Before I call you out, let me see if I understand you correctly....
> 
> Are you saying that IF there is not a negative gradient in pedal (pedal angle decreasing) i.e. pedal angle doesn't change/or increases/stays WOT, and Actual boost is greater than Requested boost, that ME7 will open DV?


Yes, it will "PWM" it.

At first it tries to reduce N75 duty cycle (PID), if boost is still too high, it will use N249, if boost is STILL too high, it will begin to close throttle body.

Call me out.

EDIT: Proper tune may disable boost diag of course.


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## elRey (May 15, 2001)

Sim said:


> Yes, it will "PWM" it.
> 
> At first it tries to reduce N75 duty cycle (PID), if boost is still too high, it will use N249, if boost is STILL too high, it will begin to close throttle body.
> 
> ...


You, sir, are wrong. ME7 doesn't NOT utilize N249 outside of a negative pedal gradient (backing off gas) or DV diagnostics. It doesn't not use DV in an overboost situation.

And you're wrong about PWM. In no case does the ECU control the N249 via duty cycle. It's on/off.


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## elRey (May 15, 2001)

Twopnt016v said:


> The DV will work faster when it has a direct vac source to the intake manifold and doesn't go thru the n249/vac canister.


The DV does have a direct vac source when the N249 is not active. Or do you mean a shorter, and larger hose? Smaller dia hose = faster. But yes, a shorter hose = faster.

I will add above the ~22psi limit of ME7, the ECU will not know if it should open the DV when letting off gas.


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## Dave926 (Mar 30, 2005)

Rey,

Off hand do you know what module in FR would have information regarding n249 operation?


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## elRey (May 15, 2001)

Dave926 said:


> Rey,
> 
> Off hand do you know what module in FR would have information regarding n249 operation?


LDUVST

B_ldsua is the variable for N249 activation


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## Dave926 (Mar 30, 2005)

Perhaps a flowchart from FR will help Sim understand when it operates?

Im going to look at it myself.


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## Sim (Jun 27, 2002)

elRey said:


> You, sir, are wrong. ME7 doesn't NOT utilize N249 outside of a negative pedal gradient (backing off gas) or DV diagnostics. It doesn't not use DV in an overboost situation.
> 
> And you're wrong about PWM. In no case does the ECU control the N249 via duty cycle. It's on/off.


Allright elRey,

You are right... You all seem to know ME7 (a lot more better than me), so let me apologize for my previous assumption(s).

Happy New Year!


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## Vegeta Gti (Feb 13, 2003)

What is this surge you speak of? ? 6 years no n249... No issues. Just did the full deletes on a buddy's stock gli. No issues. Even after the flash. 

Sent from my SPH-L720 using Tapatalk


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## Dave926 (Mar 30, 2005)

Vegeta Gti said:


> What is this surge you speak of? ? 6 years no n249... No issues. Just did the full deletes on a buddy's stock gli. No issues. Even after the flash.
> 
> Sent from my SPH-L720 using Tapatalk


Chris,

Doesnt mean the compressor surge isnt happening because you cant feel it. Vagcom isnt going to log fast enough to see it.

Data on the previous page, and in the link, proves it happens. Doesnt mean the turbo is going to snap in half either.

It completely astounds me how most of this ****ing forum cant see data as a plausible form of proof.


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## AmIdYfReAk (Nov 8, 2006)

IMO, surge will happen unless the dv opens PIROR to the throttle closing, so your high speed logs show it happening... What does that really mean for any of us?

I'm in total agreement that surge is a bad thing, but from the times turbos have been on a gas engine its been a fact of life... And for us that are running above boost levels, or larger turbos its going to happen with or without the n249 in place.

Keeping that in mind, what does it matter? What is there even to argue about?


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## Sim (Jun 27, 2002)

Dave926 said:


> Chris,
> Doesnt mean the compressor surge isnt happening because you cant feel it.


Apologies for still interfering , i am actually interested in the topic. I hope that is not a problem.

I am running mafless at the moment, so cannot verify if there is any compressor surge on my car (with no n249).
As mentioned previously i can log MAF output voltage along with MAP (with adequate sampling rate).
I will put a MAF back in the car next week and will check this and report back, OK?

A momentary pressure spike does not automatically mean compressor surge (in my opinion). Air can be compressed (thank God  ) and since we have plenty of room in between the turbo and throttle body, a delay of 0.1-0.2 second (guess) in the DV actuation will not cause compressor surge. This is my opinion and this can be verified.


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## suffocatemymind (Dec 10, 2007)

Sort of off topic - what can help with both DV response and opening operation: a "larger" ID vac hose or "smaller" ID hose? I feel like both options can be argued for...


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## suffocatemymind (Dec 10, 2007)

I've always liked the idea of the N249 and never once had a boost surge/stability/fluctuation problem with it hooked up with the 710N (which worked perfectly fine with chipped boost levels). It wasn't until I rigged up the MadMax valve (ridiculously awesome by the way) when I saw N249 malfunction codes (soft, no CEL) and fluttering at ANYTHING less than 10psi. This was most-likely due to the amount of vacuum required to cracked the valve (19 inMg). All of that COMPLETELY went away when I bypassed the N249. The N249, hoses, and clamps were all in perfect shape and leak-free. Pressure tested 20psi a few times without a hiss! Inspected it all like a hawk when removed.

The only "negative" thing I've noticed in the past 2 years post-delete has been worse fuel mileage (down 25 miles per tank) - even with a new MAF, front O2, spark plugs, and new PCV/vac hoses - and I noticed this soon after the delete, 21inMg at idle when warm. Nearly-zeroed fuel trims (haven't checked in a while though). Maybe my panel ITG just needs a really good cleaning rather than "picking out the big stuff" during OCIs. Maybe my squeaky-clean IAT sensor crapped out. Maybe I have an inaudible pinhole exh leak pre O2. Maybe one of my brakes are dragging. All I know is that definitely did it right (followed twopnt016v's thread of choice :thumbup: ) and have ZERO leaks.

Not having the ugly and bulky vac res and having a properly-functioning MadMax valve far outweigh the 25 MPT hit, if the bypass truly affects fuel mileage, that is.


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## Dave926 (Mar 30, 2005)

suffocatemymind said:


> Sort of off topic - what can help with both DV response and opening operation: a "larger" ID vac hose or "smaller" ID hose? I feel like both options can be argued for...


Good question.

Related or not, but when I had my 16v turbo the BOV would leak pretty good (via pressure test), but on a friend's VRT the same valve it would not. Difference between cars was his hose, it was much larger. 



suffocatemymind said:


> I've always liked the idea of the N249 and never once had a boost surge/stability/fluctuation problem with it hooked up with the 710N (which worked perfectly fine with chipped boost levels). It wasn't until I rigged up the MadMax valve (ridiculously awesome by the way) when I saw N249 malfunction codes (soft, no CEL) and fluttering at ANYTHING less than 10psi. This was most-likely due to the amount of vacuum required to cracked the valve (19 inMg). All of that COMPLETELY went away when I bypassed the N249. The N249, hoses, and clamps were all in perfect shape and leak-free. Pressure tested 20psi a few times without a hiss! Inspected it all like a hawk when removed.
> 
> The only "negative" thing I've noticed in the past 2 years post-delete has been worse fuel mileage (down 25 miles per tank) - even with a new MAF, front O2, spark plugs, and new PCV/vac hoses - and I noticed this soon after the delete, 21inMg at idle when warm. Nearly-zeroed fuel trims (haven't checked in a while though). Maybe my panel ITG just needs a really good cleaning rather than "picking out the big stuff" during OCIs. Maybe my squeaky-clean IAT sensor crapped out. Maybe I have an inaudible pinhole exh leak pre O2. Maybe one of my brakes are dragging. All I know is that definitely did it right (followed twopnt016v's thread of choice :thumbup: ) and have ZERO leaks.
> 
> Not having the ugly and bulky vac res and having a properly-functioning MadMax valve far outweigh the 25 MPT hit, if the bypass truly affects fuel mileage, that is.


A few of the user reported a change in mileage, though mild.

I would like to think that the vacuum reservoir is sized relative to the stock DV. That being said, I am sure that difference BOV/DV's have different sized chambers in them, and would thus require a different sized reservoir.


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## AmIdYfReAk (Nov 8, 2006)

suffocatemymind said:


> I've always liked the idea of the N249 and never once had a boost surge/stability/fluctuation problem with it hooked up with the 710N (which worked perfectly fine with chipped boost levels). It wasn't until I rigged up the MadMax valve (ridiculously awesome by the way) when I saw N249 malfunction codes (soft, no CEL) and fluttering at ANYTHING less than 10psi. This was most-likely due to the amount of vacuum required to cracked the valve (19 inMg). All of that COMPLETELY went away when I bypassed the N249. The N249, hoses, and clamps were all in perfect shape and leak-free. Pressure tested 20psi a few times without a hiss! Inspected it all like a hawk when removed.
> 
> The only "negative" thing I've noticed in the past 2 years post-delete has been worse fuel mileage (down 25 miles per tank) - even with a new MAF, front O2, spark plugs, and new PCV/vac hoses - and I noticed this soon after the delete, 21inMg at idle when warm. Nearly-zeroed fuel trims (haven't checked in a while though). Maybe my panel ITG just needs a really good cleaning rather than "picking out the big stuff" during OCIs. Maybe my squeaky-clean IAT sensor crapped out. Maybe I have an inaudible pinhole exh leak pre O2. Maybe one of my brakes are dragging. All I know is that definitely did it right (followed twopnt016v's thread of choice :thumbup: ) and have ZERO leaks.
> 
> Not having the ugly and bulky vac res and having a properly-functioning MadMax valve far outweigh the 25 MPT hit, if the bypass truly affects fuel mileage, that is.


That's interesting, I never paid much attention to people claims to fuel mileage change with the deletes...

Mine went up ~150KM/tank after all of the deletes due to a bad maf and torn hoses all over the place.


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## Vegeta Gti (Feb 13, 2003)

Dave926 said:


> Chris,
> 
> Doesnt mean the compressor surge isnt happening because you cant feel it. Vagcom isnt going to log fast enough to see it.
> 
> ...



I know I was stirring the pot lol. I logged it and it had a touch under heavy load in higher gears. I was just being an ass. 

Sorry lo

Sent from my SPH-L720 using Tapatalk


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## elRey (May 15, 2001)

AmIdYfReAk said:


> IMO, surge will happen *unless the dv opens PIROR to the throttle closing*, ...


ME7 _tries_ to do just that.


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## Sim (Jun 27, 2002)

elRey said:


> ME7 _tries_ to do just that.


EDIT: ME7 sees the future?

The throttle plate from 100% to ca.10% (where surge may begin to depelop at high airflows) closes in approximately 100-150 milliseconds. After this time, on high RPMs there will be vacuum in the intake manifold, too. For the ECU to be able to prevent surging would have to activate the n249 faster than this! I am not sure that the ECU is that fast in detecting negative throttle transients, but lets presume it is: we are still talking about a fraction of a second! N249 (as already wrote) introduces a restriction (will measure it, ill dig a valve out later) in the control line of the DV. I think that this restriction is just enough to slow things down, so all the advantages of the ECU switching sooner (if at all) are superseded.


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## elRey (May 15, 2001)

Sim said:


> EDIT: ME7 sees the future?
> 
> The throttle plate from 100% to ca.10% (where surge may begin to develop at high airflows) closes in approximately 100-150 milliseconds. After this time, on high RPMs there will be vacuum in the intake manifold, too. For the ECU to be able to prevent surging would have to activate the n249 faster than this! I am not sure that the ECU is that fast in detecting negative throttle transients, but lets presume it is: we are still talking about a fraction of a second! N249 (as already wrote) introduces a restriction (will measure it, ill dig a valve out later) in the control line of the DV. I think that this restriction is just enough to slow things down, so all the advantages of the ECU switching sooner (if at all) are superseded.


Similar to the D component of a PID controller.

Restriction (a point of smaller diameter in flow path) is an issue when flow is continuous. However, in the case of a valve (DV) , air is not continuous. The air volume in the line and volume in the valve itself (behind piston/diaphragm) is all that has to flow. Once the valve is open, no more air moves. So, ideally you want the smallest amount of volume to move in order to create a vacuum behind the diaphragm. Considering the volume we are talking about, the restriction of the N249 has no effect (IMO), But I don't have data proving that.


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## Sim (Jun 27, 2002)

elRey said:


> Similar to the D component of a PID controller.
> 
> Restriction (a point of smaller diameter in flow path) is an issue when flow is continuous. However, in the case of a valve (DV) , air is not continuous. The air volume in the line and volume in the valve itself (behind piston/diaphragm) is all that has to flow. Once the valve is open, no more air moves. So, ideally you want the smallest amount of volume to move in order to create a vacuum behind the diaphragm. Considering the volume we are talking about, the restriction of the N249 has no effect (IMO), But I don't have data proving that.


OK, i accept your argument that the restriction of the N249 may not play a major role here (due to the fact that the volume of the "actuator chamber" in the DV is relatively small), but still all the action we are discussing about here is not longer than 200ms (and this is a worst case scenario, it is faster in reality). The ECU (IMO) cant respond this fast and also there is a reaction time for the valve and air/vac in the system. EDIT: To counteract a 200ms long phenomenon, it should be at least an order of magnitude faster than that (IMO).

BTW: Do you happen to know the derivative time constant in this PID controller like thing you referred? In my (questionable) experiences if the derivation is too fast/frequent, the gain must be high and that way it does not really worth anything except for introducing noise and error in the control loop.


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## elRey (May 15, 2001)

This sounds like a fun logging exercise. With the high sample rate loggers out now, we should be able to get a fairly good idea if the DV actuation has any affect and get an idea of true event durations. 

As for the D component I mentioned, it's similar but not the same. It looks at the rate of change. It's not a complete PID. If you are insterested I can post flow diagram like Dave suggested. It would a lot easier than trying understand my attempt to explain it.


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## groggory (Apr 21, 2003)

Added to FAQ under electrical


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## Sim (Jun 27, 2002)

elRey said:


> This sounds like a fun logging exercise. With the high sample rate loggers out now, we should be able to get a fairly good idea if the DV actuation has any affect and get an idea of true event durations.


Agreed! I will do my logs in a few days.




elRey said:


> As for the D component I mentioned, it's similar but not the same. It looks at the rate of change. It's not a complete PID. If you are insterested I can post flow diagram like Dave suggested. It would a lot easier than trying understand my attempt to explain it.


Transient detection routines (all) have got a time constant (put it simple: reaction time). If you check the rate of change (delta value) too frequently, your output will be very low unless the variable you are checking is very very fast. Signal to noise ratio (error) is exponentially increasing by decreasing reaction time (lowering time constant), therefore time constants have to be chosen carefully (too slow aint good either). To tell you the truth, i have no idea how exactly ME7 is activating the N249 (and to be the honest i dont even care, as i am not using ME7), but i would call it a fail if it checked negative throttle transients.

As a rule of thumb, if you have more ways to solve a problem always use the simplest one. If i were to write the software for an engine management (*cough*), i would use a table for maximum allowed MAP vs TPS. Lets say at 50% TPS only 1600mbar is allowed, so if the pressure is more than this in the charge pipe, the N249 opens DV. As pressure falls below the threshold (-hysteresis), N249 closes DV. (EDIT: This way the ECU would not have to wait for the TB to close, it could begin venting boost even at higher throttle positions, ALSO would not vent at all if pressures are within spec (not dangerous)).
However, this may cause n249 (and DV) to open/close rapidly around the threshold pressure at higher part throttle (or full throttle) loads. This (spookily  ) reminds me how ME7 acted in my car!!!


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## Sim (Jun 27, 2002)

Another interesting question in this topic:
Why did they put the MAP sensor into the intercooler (or charge pipe in some models) instead of the intake manifold itself if they do not want to "regulate" the pressure in the charge pipe?


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## [email protected] Performance (Sep 17, 2013)

Sim said:


> Another interesting question in this topic:
> Why did they put the MAP sensor into the intercooler (or charge pipe in some models) instead of the intake manifold itself if they do not want to "regulate" the pressure in the charge pipe?


The n249 DOES regulate charge pressure spikes, and it's the primary function of the system. You are 100% correct. :thumbup:

Whether or not it slows dv response, or quickens it is open for debate. I for one don't believe that it has any positive effect with regards to performance. Upon throttle lift the intake manifold is INSTANTLY in vacum by its very nature. Whether or not certain tunes work better with the n249 is moot IMO; as it can be tuned around.


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## elRey (May 15, 2001)

[email protected] Performance said:


> The n249 DOES regulate charge pressure spikes, and it's the primary function of the system. You are 100% correct. :thumbup:


..... maybe you haven't read our whole discussion?



[email protected] Performance said:


> Whether or not it slows dv response, or quickens it is open for debate. I for one don't believe that it has any positive effect with regards to performance. Upon throttle lift the intake manifold is *INSTANTLY* in vacum by its very nature. Whether or not certain tunes work better with the n249 is moot IMO; as it can be tuned around.


Nothing is INSTANT. Everything takes time. The time may be very very small, but not instant. From the point where the throttle plate closes to the point where the engine consumes all the remaining air in the intake manifold, a small amount of time will past. The debate is whether that small amount of time where the DV remains closed has ENOUGH affect on the system to merit the addition complexity of the N249.


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## [email protected] Performance (Sep 17, 2013)

elRey said:


> ..... maybe you haven't read our whole discussion?
> 
> 
> 
> Nothing is INSTANT. Everything takes time. The time may be very very small, but not instant. From the point where the throttle plate closes to the point where the engine consumes all the remaining air in the intake manifold, a small amount of time will past. The debate is whether that small amount of time where the DV remains closed has ENOUGH affect on the system to merit the addition complexity of the N249.


I have read the entire discussion, and I truly grasp the concept; though I find it hard to believe that the N249 could possibly react fast enough to engage quicker than the vacum would accumulate once the throttle plate slams shut.

Interesting topic nonetheless :beer:


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## elRey (May 15, 2001)

The ECU 'predicts' throttle close and pressure spike. In doing so, it can (theoretically) actuate the N249 before there is vacuum in the manifold.

And for those situations where the throttle is only partially closing where there is never vacuum, but still a spike or simply more than requested in pressure, it can actuate N249 where the DV would have never opened to begin with.


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## [email protected] Performance (Sep 17, 2013)

elRey said:


> The ECU 'predicts' throttle close and pressure spike. In doing so, it can (theoretically) actuate the N249 before there is vacuum in the manifold.
> 
> And for those situations where the throttle is only partially closing where there is never vacuum, but still a spike or simply more than requested in pressure, it can actuate N249 where the DV would have never opened to begin with.


I'd like to see some n249 logs under different situations. This is intriguing to say the least


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## Sim (Jun 27, 2002)

elRey said:


> The ECU 'predicts' throttle close and pressure spike. In doing so, it can (theoretically) actuate the N249 before there is vacuum in the manifold.


This is my greatest concern here, i cannot imagine how could any ECU predict the future actions of the driver. This is just simply impossible! I this was possible, i would hack the ecu to "predict" me the winning numbers on the lottery .



elRey said:


> And for those situations where the throttle is only partially closing where there is never vacuum, but still a spike or simply more than requested in pressure, it can actuate N249 where the DV would have never opened to begin with.


I am just wondering, when will you acknowledge that what you wrote here is just exactly the same thing i am trying to explain from the very beginning. I know i may have blown the fuse with my statement about ME7 knowlege, but IMO that should not be a reason to contradict me all the time. Peace. :beer:

However, my opinion is that if you remove N249 (with all its crap) and you prevent the ECU to be able to fiddle with the pressure in the intercooler, the surge which may develop is so short in duration that it will not hurt the turbo. At the link on the the first (starting) comment they run some crazy boost (for prolonged time), i would be much more concerned about that (if i cared about the turbo al all).


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## Sim (Jun 27, 2002)

[email protected] Performance said:


> The n249 DOES regulate charge pressure spikes, and it's the primary function of the system. You are 100% correct. :thumbup:


Thanks for backing me up, Jeff! :beer:


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## Chickenman35 (Jul 28, 2006)

Found some interesting reading from VW/Audi Self Help Technical programs. 

Info on N75 valve and N249 valve starts from pages 24 thru 26:

http://www.volkspage.net/technik/ssp/ssp/SSP_207.pdf

Edit: Article above refers to SSP-198 for more information on air divertor in over-run condition. This article is a Technical paper on the 2.7 Bi-Turbo engine. Interesting reading on the 2.7 engine and divertor valve operation info starts on page 27. However, it really give any more in depth information. Stilll FWIW:

http://1977.ucoz.ua/audi_s.pdf


What I did find Most interesting is that one of the main functions of the N249 valve is to allow opening of the divertor valve at light throttle cruise conditions, where the Turbo chargers were actually producing a small amount of boost, the throttle angle was low and the MAP pressure was near 0 psi ( typically -8 psi to approx +2 psi ). Part of this scenario was to increase fuel mileage.

In this situation the DV would be opened by the Auxiliary Vacuum Tank and the N249 valve to reduce exhaust back pressure. This is required due to the very fast spooling characteristics of the BW K03/K04 series Turbocharger. Under light load cruise conditions, best fuel economy is derived by operating the charge pressure system in a Normally Aspirated condition. This is not possible using just a manifold vacuum source, but it is possible if you use an Auxiliary Vacuum Tank and the N249.

Another advantage of utilizing the N249 valve to bypass air in cruise mode is that it reduces lag if a sudden increase in power is required. ( My assumption being that the Turbine side is not choked and the Compressor side is not stalled by pushing against a pre-compressed column of air ( low throttle opening ).

I'll see if I can find that Technical article again on N249 increasing MPG vs manifold vacuum operation. It was during one of my 3:00 AM insomniac browsing secessions....


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## Chickenman35 (Jul 28, 2006)

If you start reading the Technical papers on N249 valve operation, it becomes readily apparent why the MAP sensor is placed before the throttle blades, in the Charge Pressure System ( Intercooler ) , rather than off a vacuum source in the Intake manifold.

It is to detect when the Turbochargers are producing boost in a cruise condition, low TB angle scenario. Turbo's can be producing a slight charge pressure under that situation and you do not want that. You want the engine running in NA mode to maximize fuel mileage. Thus the N249 valve and DV bypassing to essentially " Free-wheel " the Turbo.


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## Soundwave_vr6 (Oct 1, 2007)

put mine back in.

car feels better at part throttle and WOT . hits 20-21psi (uni stg 2) [was hitting 24ish w/o n249]

my dv makes more of a whooooosh noise now vs pssssssst 



¯\_(ツ)_/¯


ill leave it in and report back on fuel economy :beer:


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## Dave926 (Mar 30, 2005)

Sim said:


> Thanks for backing me up, Jeff! :beer:


2 wrongs do not make a right.

You really think a couple shade tree mechanics know better than an entire group of engineers at vw/bosch?

N249 use has little to do with helping save the turbo, those it does help.

ME7 in general works on predicting what the drivers request is.


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## [email protected] Performance (Jul 20, 2011)

The N249 is supposed to open the DV to prevent surge. It takes a second or two generate enough vacuum to open the DV when you let off the gas so the N249 comes in and helps.

Also, on the TFSI its used to vent boost at part throttle. You can even hear it on a stock car.


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## elRey (May 15, 2001)

Sim said:


> This is my greatest concern here, i cannot imagine how could any ECU predict the future actions of the driver. This is just simply impossible!


Consider the light tree at the dragstrip. Do racers launch on green? No, that launch on the last yellow 'predicting' that green will come on. Same concept. ECU seeing pedal start to back off. Based on how fast the pedal is moving (gradient), it predicts throttle will close based on driver input. In *conjunction* with pedal backing off, it watching requested and actual pressure deltas. And depending how fast both are changing (slope), it predict if they will cross in the near future.



Sim said:


> I am just wondering, when will you acknowledge that what you wrote here is just exactly the same thing i am trying to explain from the very beginning.


I'll acknowledge with two fundamental differences:

1) N249 is not used in an overboost/protective situation when other means of boost control aren't enough. 

2) N249 is only used when backing off pedal, or overrun as Chickenman35 and ME7 documentation states it. So, it will not interfere with what you want the system to do, as seems to be your gripe. (But this is debatable in the situation for partial throttle closing. Meaning N249 could open DV when partially closing throttle and you don't want it to if tune is not calibrated for you're setup.)



Chickenman35 said:


> What I did find Most interesting is that one of the main functions of the N249 valve is to allow opening of the divertor valve at light throttle cruise conditions, where the Turbo chargers were actually producing a small amount of boost, the throttle angle was low and the MAP pressure was near 0 psi ( typically -8 psi to approx +2 psi ). Part of this scenario was to increase fuel mileage.
> 
> In this situation the DV would be opened by the Auxiliary Vacuum Tank and the N249 valve to reduce exhaust back pressure. This is required due to the very fast spooling characteristics of the BW K03/K04 series Turbocharger. Under light load cruise conditions, best fuel economy is derived by operating the charge pressure system in a Normally Aspirated condition. This is not possible using just a manifold vacuum source, but it is possible if you use an Auxiliary Vacuum Tank and the N249.
> 
> ...


In 1.8T applications this function is not used (map zeroed out). At least in the 1.8T files I've seen. I'm curious if 2.7tt application utilizes it.


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## elRey (May 15, 2001)

Simple conclusion:

If you're old like me, N249 = :thumbup:

If not, N249 = :thumbdown:


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## groggory (Apr 21, 2003)

It seems like there are very good arguments to keeping the factory n249 system. However, it seems many aftermarket diverter valves don't work as well with the n249 as they do with some direct manifold pressure.

Maybe the optimal setup for a daily driver that has an aftermarket diverter valve would be some sort of upgraded n249 system. I don't know exactly what that means. I don't know why exactly aftermarket dv's don't work as well with the n249 system as they do with direct manifold pressure. I don't know if an improved setup would be upgraded hardware, modified software, or both.

Let me ask this... Why do aftermarket dv's sometimes have trouble opening with the n249 system? If this question needs refining, please feel free to refine it before answering.


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## [email protected] Performance (Sep 17, 2013)

Chickenman35 said:


> Found some interesting reading from VW/Audi Self Help Technical programs.
> 
> Info on N75 valve and N249 valve starts from pages 24 thru 26:
> 
> ...


I rest my case:thumbup:



Dave926 said:


> 2 wrongs do not make a right.
> 
> You really think a couple shade tree mechanics know better than an entire group of engineers at vw/bosch?
> 
> ...


Who are you calling a shade tree mechanic? I've been turning wrenches on these cars since the mid 90's, and spent a couple years as a VW dealer tech. That said; I never mentioned the N249 being used to "help save the turbo".

Relax the conjecture buddy:beer:


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## elRey (May 15, 2001)

groggory said:


> Let me ask this... Why do aftermarket dv's sometimes have trouble opening with the n249 system? If this question needs refining, please feel free to refine it before answering.


I'd have to see some log data before I would hazard a guess. Not that the question was directed @ me, just saying.



[email protected] Performance said:


> I rest my case:thumbup:


Remind me, what case is that? ... in light of the full discussion?


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## groggory (Apr 21, 2003)

elRey said:


> I'd have to see some log data before I would hazard a guess. Not that the question was directed @ me, just saying.


Seems like we'd need a log of intake mani pressure vs. Charge pipe pressure with a few different setups to see what's really going on.

Would be a cool test to do for sure


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## elRey (May 15, 2001)

groggory said:


> Seems like we'd need a log of intake mani pressure vs. Charge pipe pressure with a few different setups to see what's really going on.
> 
> Would be a cool test to do for sure


Though that would be optimal, it's not necessary to get a good idea of what's going on. If tests are ran the same (same stretch of road, same pedal actuation by driver to same boost levels), comparing charge pipe pressure with requested boost, throttle angle, pedal angle and N249 signal would yield usable logs. That's assuming a high sample rate logger is used. > 15 samples per sec.


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## Chickenman35 (Jul 28, 2006)

elRey said:


> In 1.8T applications this function is not used (map zeroed out). At least in the 1.8T files I've seen. I'm curious if 2.7tt application utilizes it.


The technical paper I was reading was specific to the 1.8T ( separate article from the ones I linked to ) . I came across it about two weeks ago. It may take me a while but I'll see if I can find it again.

Edit: It was very specific in the advantages of using the Auxilary Vacuum Tank and the N249 to increase fuel mileage and improve drive-ablity at light load and low throttle angles. For Compressor surge control alone, a vacuum source taken directly from the Intake manifold was quick enough and more than sufficient for that purpose. However, the N249 combined with an auxiliary vacuum tank allowed fuel mileage strategies and improvements in drive-ability ( elimination of small charge pipe fluctuations ) that are not possible with a direct connection of the DV to the Intake manifold vacuum source. 

Porsche also utilizes a very similar system. Since Porsche is part of the VAG and uses Motronics, some useful info may be available there. More research.... Yay :thumbup:


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## elRey (May 15, 2001)

Are you saying 1.8T use this function? What's written in technical papers and what the engineers decide to implement can differ. 

That's why I reference both documentation AND the code itself. Doc says the function is there, code says it's there but not used.


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## Sim (Jun 27, 2002)

elRey said:


> Are saying 1.8T use this function? What's written in techincal papers and what the engineers decide implement can differ.
> 
> That's why I reference both docementation AND the code itself. Doc says the function is there, code says it's there but not used.


Huge respect and friendly handshakes to the people who can disassemble and decipher orginal code, but they also may miss or misunderstand something. Also there are "gazillion" versions of me7 controllers (and software for them), i would not rule out a function in an other version which wasnt used in the one they checked. Just my 2 cents.


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## Sim (Jun 27, 2002)

Dave926 said:


> 2 wrongs do not make a right.
> 
> You really think a couple shade tree mechanics know better than an entire group of engineers at vw/bosch?
> 
> N249 use has little to do with helping save the turbo, those it does help.


Tell this to your "friend(s)" whom article you have put up here for discussion.



Dave926 said:


> ME7 in general works on predicting what the drivers request is.


Ah so you have read the docs!? That is not equal to know (or at least imagine) how a task or procedure is carried out in the practice.


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## [email protected] Performance (Jul 20, 2011)

opcorn:


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## Sim (Jun 27, 2002)

BTW: If N249 was *that* important, why did the (wv/bosch) engineers leave it out from the first 1.8T models?


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## Sim (Jun 27, 2002)

[email protected] Performance said:


> The N249 is supposed to open the DV to prevent surge. It takes a second or two generate enough vacuum to open the DV when you let off the gas so the N249 comes in and helps.
> 
> Also, on the TFSI its used to vent boost at part throttle. You can even hear it on a stock car.


I will do logs to prove that the vacuum from the intake manifold is instant as the TB closes.


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## elRey (May 15, 2001)

Sim said:


> but they also may miss or misunderstand something. Also there are "gazillion" versions of me7 controllers (and software for them), i would not rule out a function in an other version which wasnt used in the *one they checked*.


Very true, but it's not just one that I've checked. None the less, you're right. There might be a 1.8T ECU out there that uses it. My money says you won't find one in a untuned DBW 1.8T though.

But let's say it is used (which it's not), it's still not a function that does what's been argued here. It would only be for cruising and slight acceleration from cruise. e.g. just because I move the pedal 10% from cruise doesn't mean I want any amount of boost. So, the N249 keeps the DV open and allow NA driving around cruise.

_But here's the kicker.... if the N249 has the DV open, how can the pressure ever rise? If the pressure never rises, how does the ECU know when to close the DV? That function ONLY considers pressure and not pedal. It may have been ignored in 1.8Ts because if was never finished. BUT, this is solely going by the documentation. That catch22 situation may not exist in the code itself. I'll take a look._ <- incorrect

Edit: My mistake. That function does close DV when requested boost rises above a threshold. No catch22.



Sim said:


> I will do logs to prove that the vacuum from the intake manifold is instant as the TB closes.


Do you have a MAP after your TB?


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## Sim (Jun 27, 2002)

elRey said:


> But here's the kicker.... if the N249 has the DV open, how can the pressure ever rise? If the pressure never rises, how does the ECU know when to close the DV? That function ONLY considers pressure and not pedal. It may have been ignored in 1.8Ts because if was never finished. BUT, this is solely going by the documentation. That catch22 situation may not exist in the code itself. I'll take a look.


Well, lets say you are cruising with 15% TPS and there is 1600mBar pressure in the charge pipe. ECU wants less in it (why not?), so it opens DV with the n249. Pressure begins to fall rapidly, but as it is below the prestored threshold (for the given TPS), ECU closes DV and pressure may build up again. It is that simple (imo). (BTW i have already visioned a scenario like this before)


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## Sim (Jun 27, 2002)

elRey said:


> Do you have a MAP after your TB?


Not, ... Yet :laugh:


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## Sim (Jun 27, 2002)

By the way, if somebody is using a BOV there is no need for complete vac to open it, since the pressure in the charge pipe pushes it upwards. As the pressure in the upper nipple decreases and reaches pressure in the charge pipe - spring tension, the BOV will begin to open. This is not necessarily negative pressure.

EDIT: This may also apply to DV-s (blown from sideways, too).


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## carsluTT (Dec 31, 2004)

goodness....... lots of pro con info. ill be doing something soon about this just not sure what


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## Chickenman35 (Jul 28, 2006)

Sim said:


> BTW: If N249 was *that* important, why did the (wv/bosch) engineers leave it out from the first 1.8T models?


Because they were using the ME 5.92 which did not have the capabilities of the ME 7 ECU. ME 5.92 being DBC was a a major disadvantage . From what I have read, most of the enhancements were due to the hugely extended capabilities offered by DBW and the extra computing power of the ME7.

Edit: And the first 1.8T models using the ME 5.92 ECU ( AEB primarily ) did not use a MAP sensor at all ...which is essential to the control of the N249 system. CAFE numbers were also becoming more and more important, so engineers began exploiting every method possible to increase fuel mileage. Researching EPA fuel mileages shows a correlation in increased fuel mileage between identical models ( A4 for example ), when the engineers switched from the ME5.92 to the ME7.


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## groggory (Apr 21, 2003)

If anyone's willing to put the leg work in, I'd love to see some logging on a stock frame turbo car with all the stock stuff. Then do the logging again with something like a Forge 007 + green spring. Then do the logging again with the N249 bypassed and the DV running straight to manifold.

I'm not sure exactly what logging is necessary here...but it seems some hard data in this discussion could settle lots of things...as long as that data is chosen and collected in a scientific unbiased manner.


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## Dave926 (Mar 30, 2005)

groggory said:


> If anyone's willing to put the leg work in, I'd love to see some logging on a stock frame turbo car with all the stock stuff. Then do the logging again with something like a Forge 007 + green spring. Then do the logging again with the N249 bypassed and the DV running straight to manifold.
> 
> I'm not sure exactly what logging is necessary here...but it seems some hard data in this discussion could settle lots of things...as long as that data is chosen and collected in a scientific unbiased manner.


Agreed.

Data would need to be taken with an external controller, since the stock map caps out so low.


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## Chickenman35 (Jul 28, 2006)

groggory said:


> If anyone's willing to put the leg work in, I'd love to see some logging on a stock frame turbo car with all the stock stuff. Then do the logging again with something like a Forge 007 + green spring. Then do the logging again with the N249 bypassed and the DV running straight to manifold.
> 
> I'm not sure exactly what logging is necessary here...but it seems some hard data in this discussion could settle lots of things...as long as that data is chosen and collected in a scientific unbiased manner.


^ Agreed. And isn't it refreshing to have a technical discussion that hasn't degraded into the " normal " Vortex shenanigans :thumbup::laugh:


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## Slimjimmn (Apr 8, 2006)

Twopnt016v said:


> When I purchased the car used it had stock DV and had the issue. I swapped a know good stock unit and still had issue. I pulled an APR R1 valve off another car and it still did the same thing. I bypassed the n249( after trying a new n249) and the problem went completely away. The n249 was being sent a signal by the ecu to bleed off boost and the valve would actuate the DV while on part throttle causing surging. I agree the DV needs to have a proper vac source and there is not one better than straight off the intake manifold. Right now I am running the MadMax DV in push orientation meaning the DV is flipped around from how it is stock so boost pressure and a solid vac source are opening the valve vs just having a vac supply to actuate it. No part throttle issues, no boost leaks, super quick DV actuation with lighting fast recovery speed.


I use a R1 and have no issues. 
The n249 was installed by VW as a safety device to limit boost if the n75 can not regulate pressure. 
Other than obviously used to open the dv for normal operation. 

I DID have issues with my n249 installed and a forge (and also forge style of brand) causing part throttle issues. I do not think the n249 should be deleted with piston style dv or bov.

Also vw (and all other mnfr) switched to electronic dv because of maintenance parts. But every tsi/fsi owner has learned they still fail just as often due to oil residue and vapors in the intake tract from poor pcv design.


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## codergfx (Jan 11, 2009)

Always had my n249 and n112 bypassed never had issues with it. The DV response became better actually running direct vacuum


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## Sim (Jun 27, 2002)

Chickenman35 said:


> Because they were using the ME 5.92 which did not have the capabilities of the ME 7 ECU. ME 5.92 being DBC was a a major disadvantage . From what I have read, most of the enhancements were due to the hugely extended capabilities offered by DBW and the extra computing power of the ME7.
> 
> Edit: And the first 1.8T models using the ME 5.92 ECU ( AEB primarily ) did not use a MAP sensor at all ...which is essential to the control of the N249 system. CAFE numbers were also becoming more and more important, so engineers began exploiting every method possible to increase fuel mileage. Researching EPA fuel mileages shows a correlation in increased fuel mileage between identical models ( A4 for example ), when the engineers switched from the ME5.92 to the ME7.


I knew that somebody will give me just exactly this answer (me3.8.x however), but this is just not what i meant. The turbos (k03) were practically identical, but still they did not even think about hurrying up opening the dv to prevent compressor surge. I have no idea how many AEB-s and AGU-s (etc) have been manufactured, but they were good enough (with no n249) for VW and Bosch to write their names on them. IMO this is just another nail in the coffin of the original theory (which started this topic).

Most of us are coming here to squeeze out more (or even maximum) power out of our cars (correct me if i am wrong), and not because we are interested in preserving our cars in their original ("failsafe") state.


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## Sim (Jun 27, 2002)

groggory said:


> In a scientific unbiased manner.


I am completely scientific and completely unbiased!


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## Sim (Jun 27, 2002)

Here is an interesting log from my "treasure chest". A bit of explanation is needed for sure. This is a log of an ordinary cruise (in 3rd gear IIRC) with a moded 1.8t (AUM). 2.5" CAI, 2.5" exhaust piping (singe pass thru muffler, no cat), TFSI turbo, big FMIC, BOV, no N249. BOV vac is directly sourced from the intake manifold.

What should be seen here is that the throttle is slowly opened and that the MAP (which is located in the intercooler piping) shows a high boost of 1.2 Bar even at 2620RPM. This turbo is of course not capable of producing +1.2bar on 2620RPM (full throttle). The MAP is just showing an increased pressure in the charge piping, because the engine is choked (only 34% TPS max.) + RPMs are quite low, therefore engine has low "air demand". This (still pretty small) turbo is so "efficient" in this area that it will continue to push more and more air into this choked system, even with a relatively constant tps (28-34%) the pressure in the charge piping is just increasing and increasing until finally the BOV opens (we could hear it) and releases the excessive pressure.

But, why did the BOV open?
The BOVs and DVs get their vacum source from the intake manifold (from after and not from before the throttle body). Due to the throttle body being partially open, there will be a pressure difference in the intake manifold and charge piping. Saldy there is no log of the actual difference, but it may have been big enough to push the piston of the BOV up! How? At the upper part in the BOV/DV (above the piston/diaphragm) the pressure will be equal to the pressure in the intake manifold (lower pressure), but the pressure acting against the piston from below will be equal to the pressure in the charge piping (higher pressure). If the pressure difference is higher than what the spring in the BOV/DV can withstand (EDIT: also considering pistons upper and lower surface area ratio if it is not equal), the valve will open causing a noticable jerk.

In this particular case the phenomenon got amplified by a tuning "mistake", which let the wastegate (theres a ~7psi actuator in it however) to open too widely for these low TPS-es. Decreasing the N75 duty cycle down to 17% could not stop pressure buildup either! If the BOV could withstand higher pressures, i guess (!!!) the pressure buildup could continue to accelerate until the turbo reached its surge limit.

K03-s are all considered to be small and efficient turbos for these low part throttle airflows, so the same thing may happen without "regulated/limited" charge pipe pressure ALONG with weaker BOV/DV springs.

I would like to point out another important feature of the log: there are no negative throttle transients visible (EDIT: during pressure buildup),


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## elRey (May 15, 2001)

Chickenman35 said:


> What I did find Most interesting is that one of the main functions of the N249 valve is to allow opening of the divertor valve at light throttle cruise conditions, where the Turbo chargers were actually producing a small amount of boost, the throttle angle was low and the MAP pressure was near 0 psi ( typically -8 psi to approx +2 psi ). Part of this scenario was to increase fuel mileage.
> 
> In this situation the DV would be opened by the Auxiliary Vacuum Tank and the N249 valve to reduce exhaust back pressure. This is required due to the very fast spooling characteristics of the BW K03/K04 series Turbocharger. Under light load cruise conditions, best fuel economy is derived by operating the charge pressure system in a Normally Aspirated condition. This is not possible using just a manifold vacuum source, but it is possible if you use an Auxiliary Vacuum Tank and the N249.
> 
> I'll see if I can find that Technical article again on N249 increasing MPG vs manifold vacuum operation. It was during one of my 3:00 AM insomniac browsing secessions....





Chickenman35 said:


> It is to detect when the Turbochargers are producing boost in a cruise condition, low TB angle scenario. Turbo's can be producing a slight charge pressure under that situation and you do not want that. You want the engine running in NA mode to maximize fuel mileage. Thus the N249 valve and DV bypassing to essentially " Free-wheel " the Turbo.


No where in those technical studies did it mention N249 activation during cruise. I believe you're getting that info from S4Wiki whose references are other ppl's posts (e.i. word of mouth, regurgitate) Though, there MIGHT be an original, reliable source. I didn't find it. Again, the function is there, just not used in 1.8T application.




Slimjimmn said:


> The n249 was installed by VW as a safety device to limit boost if the n75 can not regulate pressure.





Sim said:


> and not because we are interested in preserving our cars in their original ("failsafe") state.


More regurgitated info. N249 is NOT used as fail-safe, or safety device.




Sim said:


> I knew that somebody will give me just exactly this answer (me3.8.x however), but this is just not what i meant. The turbos (k03) were practically identical, but still they did not even think about hurrying up opening the dv to prevent compressor surge. I have no idea how many AEB-s and AGU-s (etc) have been manufactured, but they were good enough (with no n249) for VW and Bosch to write their names on them. IMO this is just another nail in the coffin of the original theory (which started this topic).


Typically newer generations are improvements over old ones. AEB/AGU vs AWP/AWB. That argument could be used for why they never used Direct Injected Diesel engines in horse drawn wagons. It does prove that the turbo won't fall apart when N249 is deleted. What it doesn't say is N249 does nothing to extend turbo life.




Sim said:


> Most of us are coming here to squeeze out more (or even maximum) power out of our cars (correct me if i am wrong), ...


Funny thing is, according to VAG the N249 was added to increase performance. :laugh:


From VAG, not just repeating someone else's forum posted info:



VAG technical study 207 on TT said:


> The turbocharging system comprises the following
> components:
> – Exhaust emission turbocharger
> – Charge air cooler
> ...


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## elRey (May 15, 2001)

Sim said:


> ....
> I would like to point out another important feature of the log: there are no negative throttle transients visible (EDIT: during pressure buildup),
> 
> http://www.ignitronecu.com/pictures/vortex_bovopens.jpg


Was the N249 equipped?


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## Sim (Jun 27, 2002)

elRey said:


> Was the N249 equipped?


No.


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## elRey (May 15, 2001)

So then, the way I read your post (please correct me if I'm wrong) is that what people are perceiving as ECU opening DV during part-throttle causing surging/bucking (not-compressor surge) is possibly not the N249's fault.


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## Sim (Jun 27, 2002)

elRey said:


> Funny thing is, according to VAG the N249 was added to increase performance. :laugh:


Funny, indeed. IMO, the pressure at maximum performance (100% TPS) is just about to be the same before and after throttle body.


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## elRey (May 15, 2001)

overall performance vs peak performance


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## Sim (Jun 27, 2002)

elRey said:


> So then, the way I read your post (please correct me if I'm wrong) is that what people are perceiving as ECU opening DV during part-throttle causing surging/bucking (not-compressor surge) is possibly not the N249's fault.


Without logging the actual car i would not make any statements (like that), though it may be one possible reason, yes.
N249 in practice could help keeping the the pressure in the charge pipe low(er)., EDIT: of course actuated by the ECU itself. If venting excessive boost happens earlier, may not be that noticeable in theory.

TBH, i do not see any other reason for the N249 to be there.
On BT cars, where they are happy if boost developes by 5k RPMs and100% TPS (way outside cruising conditions) i find N249 completely unneccesary. But thats only me.

EDIT2: The main reason for posting that log is that excessive pressure CAN build up without negative throttle transients (on the contrary: at positive transients, too)


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## Sim (Jun 27, 2002)

Also, with careful N75 mapping (and no n249), pressure buildup (on part throttle) may be limited. But tell me honestly, which tuner will decrease duty cycles (anywhere in the map)?!


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## elRey (May 15, 2001)

Sim said:


> EDIT2: The main reason for posting that log is that excessive pressure CAN build up without negative throttle transients (on the contrary: at positive transients, too)


I agreed, but ECU will not activate N249 in those situations.


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## Sim (Jun 27, 2002)

elRey said:


> I agreed, but ECU will not activate N249 in those situations.


OK, but why is it there then?
To keep the DV open (turbo bypassed) until driver applies a more generous amunt of throttle? As seen, pressure in the charge pipe can skyrocket even at 30+% TPS! Days are passing away until i press the pedal more than that. I would not be happy at all if i had a turbo car with the turbo on it bypassed during normal cruise.


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## elRey (May 15, 2001)

Sim said:


> As seen, pressure in the charge pipe can skyrocket even at 30+% TPS! Days are passing away until i press the pedal more than that. I would not be happy at all if i had a turbo car with the turbo on it bypassed during normal cruise.


Look at your N75 duty cycle in that log as 'pressure in the charge pipe can skyrocket'. Your throttle angle is increasing while your N75 duty is decreasing. That's suppose to be your boost control. Why it's not keeping pressure in check is a whole other subject. But it's not the job of the N249.


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## rstolz (Jun 16, 2009)

the first page reads the same as the third...

Need the N249? Nope. Want it? that depends

The discussion is basically one of DV *Response* versus DV *Control*

Track car or drag car? ditch the N249. The N249's greatest function is under partial throttle. Under WOT or NOT, it's basically just a delay, something to slow down the Vac from opening the DV.

Street car? up to the user. mildly more smooth and better efficiency and mpg, and mildly slower DV response. Sure The N249 reduces air turbulence, but it also slows overall DV response, albeit fractionally; can you live with that?

my 2 cents

Turbo life? really, who cares; the difference is negligible or too hard to prove.


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## elRey (May 15, 2001)

rstolz said:


> Under WOT or NOT, it's basically just a delay, something to slow down the Vac from opening the DV.
> 
> ....but it also slows overall DV response,


What are these statements based on?

It's been argued that the ECU can open the DV BEFORE manifold sees vacuum. Thus allowing DV to respond FASTER with N249. That contradicts your statements.

Also what about the N249's function of reducing turbo lag on respool between shifts? Sounds applicable to 'track car or drag car'.


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## Sim (Jun 27, 2002)

rstolz said:


> the first page reads the same as the third...
> 
> Need the N249? Nope. Want it? that depends
> 
> ...


Agreed! This topic should be renamed to "Discussion about the function of the N249" .


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## elRey (May 15, 2001)

Great, then let me start:

The purpose/function of the N249 is to reduce turbo lag and improve respool between shifts, thus improve performance.


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## Sim (Jun 27, 2002)

elRey said:


> Also what about the N249's function of reducing turbo lag on respool between shifts? Sounds applicable to 'track car or drag car'.


I must be retarded, probably that is the reason why i cannot see how N249 could help turbo respool on a 1/4 mile strip.

Usually RPMs are high (6000+) at the shift point, so as throttle body approaches the lower10% there will be vacuum (less than 1000mBar) in the intake manifold, too. As discussed previously this is achieved in a fraction of a second. Do not tell me that ME7 will predict when will I let off throttle from 100%, even before i would know about it!!! I do not want to repeat myself (it hurts even for me by now), but you seem to be repeating the same (let me apologize in advance) stupid things again.

Opening DV before (!) closing the electric throttle body is the only way to do this, which would practically mean an intended dealy or slowdown of throtle plate movement. Now this would be another fail, also quite unwanted feature in a race car. All the race cars i met with over here are using ALS to help turbo "respool", opening BOV/DV is considered to be a mistake on the track/strip. Maybe i am living at the wrong place.


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## elRey (May 15, 2001)

Clarify something for me. Are you arguing that I fabricated all this and there is not a function in ME7 1.8T that tries to open the DV as early as possible even before manufold vacuum based on negative pedal gradient and change in reguested vs actual pressure? Or just that the ECU tries but fails because there's not enough time for the DV to open any earlier?

If the former then we have more arguing to do. If the latter then there's nothing more to say and only unbais, emperical data can prove one way or the other. But it seems to me that VAG/bosch engineers might have thought to do that (collect and evaluate data) before deciding to implement the system.


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## rstolz (Jun 16, 2009)

statement are based on understanding of basic mechanical and engineering properties and forces. 



> Also what about the N249's function of reducing turbo lag on respool between shifts?


bull-honky. in a WOT application a direct connection will function more efficiently. in a partial throttle application, yes, opening the valve to introduce more air to the TIP while simultaneously reducing charge pressure will help maintain spool. 



> It's been argued that the ECU can open the DV BEFORE manifold sees vacuum. Thus allowing DV to respond FASTER with N249. That contradicts your statements.


I am incredibly skeptical of this. at best, maybe it matches time with sensors, solenoids and wiring all operating at peak efficiency.

If that is, in fact, the case, then you let your foot off the pedal, and at that instant simultaneous signals are sent to the TB and the N249. The throttle plate closes, causing instantaneous vacuum in the manifold, also simultaneously the N249 opens, using the reservoir to open the DV.

Now, in a mechanical connection the throttle plate closes sending a surge of vacuum to the DV, opening it.

the only way the N249 could open sooner is if there is logic that will send the signal to the N249 at a percentage of the throttle plate closing, prior to full closure, say 5%. Of course this poses a problem; any time the throttle would be at 5% the N249 would be trying to open, so there would need to be more logic written in to determine that the pedal isn't being held at 5%, but instead was dropped to 5% from some parameter that was written in... Should it trigger if throttle drops from 80%? 100%? How quickly does the drop need to be? 

You see the difficulty in having the computer "Anticipate" your actions? It doesn't so much anticipate as run the situation through a series of parameters, and every scenario would need to be considered.

Not that it can't be done, just poses more difficulty than seems worth it,


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## rstolz (Jun 16, 2009)

on another note,

every design quirk and every detail of the 1.8T was for a single purpose. VAG wanted the first small bore turbo ULEV engine.

EVERY component, process, and parameter was designed with this single goal. The fact that it ended up being so power hungry was a happy coincidence.


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## Sim (Jun 27, 2002)

elRey said:


> Clarify something for me. Are you arguing that I fabricated all this and there is not a function in ME7 1.8T that tries to open the DV as early as possible even before manufold vacuum based on negative pedal gradient and change in reguested vs actual pressure? Or just that the ECU tries but fails because there's not enough time for the DV to open any earlier?


My opinion is that the primary function of N249 is to limit the pressure in the charge pipe under part throttle applications (full throttle can be considered as a high part throttle situation) including increasing loads, too.

You say, that the primary function of the N249 is to open DV faster than it would without it.
1. There is no need to do that, vac from the manifold will do that fast enough.
2. It cannot be carried out from full throttle (impossible), only with using a delay of the TB. I doubt that engineers implemented a delay for this, causing other side effects.

As i think our opinions will not get closer to each other, we may just end our arguments here. Peace! :beer:


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## elRey (May 15, 2001)

rstolz said:


> statement are based on understanding of basic mechanical and engineering properties and forces.


Please be more specific for the sake of this technical discussion. Which basic mechanical and/or engineering properties and forces lead you to believe the N249 slows the response of the DV?





rstolz said:


> bull-honky. in a WOT application a direct connection will function more efficiently. in a partial throttle application, *yes, opening the valve to introduce more air to the TIP while simultaneously reducing charge pressure will help maintain spool.*


What specifically differs between WOT and partial throttle THAT makes N249 less efficient one than the other? More directly, what makes the bolded statement true for partial throttle and not WOT?




rstolz said:


> I am incredibly skeptical of this. at best, maybe it matches time with sensors, solenoids and wiring all operating at peak efficiency.
> 
> If that is, in fact, the case, then you let your foot off the pedal, *and at that instant simultaneous signals are sent to the TB and the N249*. The throttle plate closes, causing instantaneous vacuum in the manifold, *also simultaneously the N249 opens, using the reservoir to open the DV.
> *
> ...


Bolded = true.

Red = incorrect.

Blue = debatable.

N249 is activated based on pedal GRADIENT not absolute position. i.e. it detects a decreasing in pedal (-1.953% to be specific). So, when ECU sees driver let off gas by only 1.95 % (whether it be from WOT, 80%, 50%, 30%, etc) AND ECU sees slope of actual boost possible crossing slope of requested boost, BOOM!!!! ECU opens DV.

Everyone keeps using the word INSTANT to describe how fast manifold sees vacuum once driver starts to let off gas. If you have an understanding of basic mechanical and engineering properties and forces, please explain how anything with mass can INSTANTLY move from point A to point B?


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## elRey (May 15, 2001)

People, I'm looking at the code. It's right here in front of me. I have logged the signal the ECU sends to the N249. I have multiple VAG documents stating the function of the N249. That is what I'm basing my arguments on, including an 'understanding of basic mechanical and engineering properties and forces'.


.....


What are you basing yours on?


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## Sim (Jun 27, 2002)

elRey said:


> What are you basing yours on?


My own experience and common sense.

I havent looked into the code (actually did back in 2004 to find the checksums so ill be able to hack my car).
I havent readed ME7 docs (dont really care, as i am already running my own ECU in my car).


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## elRey (May 15, 2001)

Sim said:


> I havent looked into the code (actually did back in 2004 to find the checksums so ill be able to hack my car).


Ah, so you've specifically looked at the N249 control subfunctions in the code and isolated the setting of bit variable B_ldsua by the states of bit variables B_ldsuad and B_ldsuas? And your arguments are partially based on what you found there?


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## Sim (Jun 27, 2002)

elRey said:


> Ah, so you've specifically looked at the N249 control subfunctions in the code and isolated the setting of bit variable B_ldsua by the states of bit variables B_ldsuad and B_ldsuas? And your arguments are partially based on what you found there?


No.


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## elRey (May 15, 2001)

So...... that leaves your experience and common sense. Got it. So, your experience includes data where you've logged the signal from ECU to N249 telling you definitively when it opens the DV vs something else like manifold vacuum?


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## Sim (Jun 27, 2002)

elRey said:


> So...... that leaves your experience and common sense. Got it. So, your experience includes data where you've logged the signal from ECU to N249 telling you definitively when it opens the DV vs something else like manifold vacuum?


No. Havent logged N249.


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## rstolz (Jun 16, 2009)

I appreciate the specific information adding to my understanding; so the DV opening is based on the ECU registering a throttle release slope of 1.953% AND actual boost must cross Requested boost. That's an interesting way around having to write in a crapload of set parameters. 


Now a question, since you can clearly read the code easily:
At WOT you're in open-loop, does open-loop affect the operation of the N249? Or does it operate the same whether in closed or open loop?



Everyone understands that instantaneous isn't really instantaneous, it's just usually so close as to not matter. like ignoring air friction in basic physics.


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## elRey (May 15, 2001)

rstolz said:


> so the DV opening is based on the ECU registering a throttle release slope of 1.953% AND actual boost *'predicted' to* cross Requested boost. That's an interesting way around having to write in a crapload of set parameters.


More specifically it takes the change in actual pressure (slope), multiples it by 3, then compares that exaggerated delta to a threshold map. Input to the map are RPM and requested pressure.
So, if actual pressure change (current pressure - previous read pressure) * 3 > 200hPa AND negative pedal gradient = open DV. So, it actual doesn't HAVE TO cross requested. It was just easier to state it that way. So, more correct generalization would be to say if actual pressure rises/changes too much + pedal back off = open DV.



rstolz said:


> At WOT you're in open-loop, does open-loop affect the operation of the N249? Or does it operate the same whether in closed or open loop?


By open-loop, do you mean boost control or lambda control?





rstolz said:


> Everyone understands that instantaneous isn't really instantaneous, it's just usually so close as to not matter. like ignoring air friction in basic physics.


Thank you. Now the debate can move on to exactly how much time does it take, how fast can the ECU read, process, react and is all that really not fast enough to intervene via N249.


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## Sim (Jun 27, 2002)

elRey said:


> Thank you. Now the debate can move on to exactly how much time does it take, how fast can the ECU read, process, react and is all that really not fast enough to intervene via N249.





elRey said:


> if actual pressure change (current pressure - previous read pressure) * 3 > 200hPa


OK, lets move on.
Do you happen to know what is the distance (time constant) between current pressure and previous read pressure? If it is more than 150ms (the duration of throttle plate closing from 100% to ~5%) then ECU will miss the event. The function has to be executed (the time constant must be) at least 10x faster than 150ms. Also are there any filter(s) applied on the current pressure variable (which may add an additional delay in signal processing)?

EDIT: Code optimization wasn't their strength for sure . They could have spared a multiplication (*3) by applying that on the prestored map itself.


----------



## Chickenman35 (Jul 28, 2006)

elRey said:


> No where in those technical studies did it mention N249 activation during cruise. I believe you're getting that info from S4Wiki whose references are other ppl's posts (e.i. word of mouth, regurgitate) Though, there MIGHT be an original, reliable source. I didn't find it. Again, the function is there, just not used in 1.8T application. (Snip)


This was not from a Wiki or someone other people word of mouth. As I stated this was a Technical paper, *from Audi*, on the developments and engineering of the 1.8T. And as I stated I will try and dig back and find it. Until I can do so, I have absolutely Zero reason to expect anyone to take this as a Truth. So please give me some time to find the relevant article again. 

I've been dealing with some major health issues in the last month, so this Forum is not really my #1 priority right now, but I'll try and look some more over the weekend.

I will reiterate this though. NONE of the design advantages of the N249 ( as quoted by Audi ), over direct manifold connection, were in regards to WOT or any large load conditions. All were very small gains that were found in drive-ablity and fuel mileage at LOW levels of load and throttle input...* and with STOCK systems *. That last bit is very important. Any alteration beyond STOCK conditions would probably throw any benefits out of the window, and talking about spool recovery times at WOT is basically irrelevant..... from what I have been able to research and IMHO of course.


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## elRey (May 15, 2001)

Sim said:


> OK, lets move on.
> Do you happen to know what is the distance (time constant) between current pressure and previous read pressure? If it is more than 150ms (the duration of throttle plate closing from 100% to ~5%) then ECU will miss the event. The function has to be executed (the time constant must be) at least 10x faster than 150ms. Also are there any filter(s) applied on the current pressure variable (which may add an additional delay in signal processing)?


10ms for delta actual pressure. Seems to fit your requirements. And yes, there is a filter on the current, actual pressure variable. As for pedal gradient, there is no time constant. Only the time between main code loops in programing. However, like most inputs, there is a filter on the pedal position variable used to calc pedal gradient.





Chickenman35 said:


> This was not from a Wiki or someone other people word of mouth. As I stated this was a Technical paper, *from Audi*, on the developments and engineering of the 1.8T. And as I stated I will try and dig back and find it. Until I can do so, I have absolutely Zero reason to expect anyone to take this as a Truth. So please give me some time to find the relevant article again.
> 
> I've been dealing with some major health issues in the last month, so this Forum is not really my #1 priority right now, but I'll try and look some more over the weekend.
> 
> I will reiterate this though. NONE of the design advantages of the N249 ( as quoted by Audi ), over direct manifold connection, were in regards to WOT or any large load conditions. All were very small gains that were found in drive-ablity and fuel mileage at LOW levels of load and throttle input...* and with STOCK systems *. That last bit is very important. Any alteration beyond STOCK conditions would probably throw any benefits out of the window,


I sorry to hear about you situation. I won't push as hard as I do the others. Setting aside finding reference on cruise operation for now, below are quotes from your referenced technical docs AND ME7 doc:

Edit: reference to N249 function can also be found in SSP_332 (A3 2.0T FSI) and SSP_337 (2.0T FSI). Both state no more, no less than what you see below. e.i. improved respool



VAG technical study 207 on TT said:


> The turbocharging system comprises the following
> components:
> – Exhaust emission turbocharger
> – Charge air cooler
> ...





VAG technical study 198 on 2.7TT said:


> Divert air control in overrun: The Motronic ME 7.1 activates the electric divert air valve for the turbocharger and opens the pneumatic divert air valves using this vacuum.
> 
> To avoid pumping the exhaust gas turbochargers *when a sudden transition from high load to overrun is made*, two divert air valves are used.
> 
> ...





ME7 Doc somewhat google translated said:


> This function serves to actuate a solenoid valve in the vacuum control line to the diverter valve .
> It is electric with inactive electronic control B_ldsua = 0, the intake manifold pressure and is active . Control B_ldsua = 1
> a separate vacuum from Vorratsbehalter on the control line to the air valve .
> By this arrangement, elec. defines the air control valve to be opened , but they are not necessarily closed , since
> ...



Please highlight where in that text you are reading N249 function only applies to low load conditions. Or please quote text from same docs that I missed.






Chickenman35 said:


> ... and talking about spool recovery times at WOT is basically irrelevant..... from what I have been able to research and IMHO of course.


And this is what seems to be escaping me. I've ask a couple of you this.... what about a WOT condition (WOT, let off gas to shift, back to WOT) negates the debatable respool advantages of the N249 on partial throttle condition?

If the N249 helps maintain compressor wheel speed during a part throttle shift, how does it NOT help do the same on a WOT shift?

Edit: I hope there's not confusion around the term 'WOT condition/situation'. I'm not saying that the N249 is use during WOT (pedal held down), but when there is any let off, partial or complete, of the pedal while WOT or high load. e.g. gear change


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## Sim (Jun 27, 2002)

elRey said:


> like most inputs, there is a filter on the pedal position variable used to calc pedal gradient.


Of course. That is also an important one which should not be negleced and may slow down the reaction of the ECU (however that slows down throttle plate, too).



elRey said:


> Edit: reference to N249 function can also be found in SSP_332 (A3 2.0T FSI) and SSP_337 (2.0T FSI). Both state no more, no less than what you see below. e.i. improved respool


Please do not mix TFSI here, as that DV is not operated pneumatically, therefore it is not connected directly to vacuum/boost on the mainfold. They HAVE to use it to prevent compressor surge as its primary task, TFSI DV will not open automatically whilst the one in the 1.8T will!

These SSP-s are quite nice to understand the basics, which were written (AFAIK) to help mechanics and technicians how to find problems and help repair cars in the shop. This (we are arguing about) is already out of scope of these papers.

I am a bit concerned (but probably that is only me) that you may have missed a portion of the code.You speak (write) about the whole ROM/code like if you were developed that, and your rhetorical style does not help either. 
The comments i write are all based on my experiences in practice, like for example hearing alu forge DV "rattling" during acceleration WITH n249 (EDIT: and not rattling without) or doing better 1/4 mile runs WITHOUT n249, etc.

Anyhow I will (try) to focus on the original question from now on; doing logs of real manifold pressure vs intercooler pressure and DV actuation speed (from full throttle) WITHOUT N249.


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## clrwatrtom (Jan 31, 2013)

*Fascinating Thread*

Good morning, i have to admit that most of what i have read in this thread is beyond my ability to understand, but if i have hurt my fuel economy by deleting the N249, i would like to get it back. 
I have an 03TT coupe 180FWD that has a 3"DP and hiflow cat with a 2 1/2" exhaust with a turbo muffler, a silicone TIP, Newsouth performance intake manifold gasket, adjustable spring pressure DV, alloy catch can, SAI Delete and EVAP Delete. If i were to re-install my Vacuum reservoir and N249, how would i tie it into my existing setup? Are there any diagrams that would show me how to connect the N249 and resevoir to my current setup? 
I appreciate any help one or all may have and hats off to you folks that have contributed to this thread as although i am still overwhelmed and confused, am am better educated about this topic than i was before reading this thread.
Thanks, tom


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## elRey (May 15, 2001)

Sim said:


> These SSP-s are quite nice to understand the basics, which were written (AFAIK) to help mechanics and technicians how to find problems and help repair cars in the shop. This (we are arguing about) is already out of scope of these papers.


And why would they leave out what you say is a primary function of the N249 from a paper that is suppose to help a mechanic find operating issues with a vehicle? However, I'm fine with leaving the SSP docs out of this. If I do, them seems to reason the other side of the argument should also.



Sim said:


> I am a bit concerned (but probably that is only me) that you may have missed a portion of the code.You speak (write) about the whole ROM/code like if you were developed that, and your rhetorical style does not help either.
> The comments i write are all based on my experiences in practice, like for example hearing alu forge DV "rattling" during acceleration WITH n249 (EDIT: and not rattling without) or doing better 1/4 mile runs WITHOUT n249, etc.



And this is what i comes down to.... my ability to reverse engineer, read, and analyze code vs your ability to analyze and grasp the whole complex system by ear and seat of pants performance preception.

I'm welcome to hear anyone else in the community that also reverse engineers the ME7 what they have found. In fact I'm very surprised noone else has bothered to add to the code reading side of the argument (for or against me).


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## Sim (Jun 27, 2002)

elRey said:


> And this is what i comes down to.... my ability to reverse engineer, read, and analyze code vs your ability to analyze and grasp the whole complex system by ear and seat of pants performance preception.


You won.


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## elRey (May 15, 2001)

Sim said:


> You won.


But I don't want to win simply by the other side getting tired and giving up. 

I can't argue that there are many testimonies of people that have removed the N249 and claim performance and whatnot. 
And I can't just assume they are just attributing what they feel/hear unnecessarily to N249 del because of lack of experience. 

But how many times have we all (all ranges of experience) gone to diagnosis an issue or change a behavior of the car by changing something, only to find what we thought we heard/felt was something different? And then change something else, and then something else? Or we change 2 or 3 things at one time and then attribute the fix/performance gain to one change forgetting about the other changes. 

I have to weight ^ that, with anything I hear as testimony without hard data.



Hoping to make things easier, we are currently discussing WHEN the N249 is used. That part should be really easy to prove with simply logging of the N249 signal. 

Once that is settled, we can move on to whether it has any real world affect.

And keeping with 'when N249 is used' part of the discussion, and trying to pull you back in....



Sim said:


> The comments i write are all based on my experiences in practice, like for example hearing alu forge DV "rattling" during acceleration WITH n249 (EDIT: and not rattling without) or doing better 1/4 mile runs WITHOUT n249, etc.


Is it remotely possible you had a faulty N249 or N249 hoses/lines/checkvalves that allowed vacuum to reach the forge DV causing rattling instead of the ECU?


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## Sim (Jun 27, 2002)

elRey said:


> Is it remotely possible you had a faulty N249 or N249 hoses/lines/checkvalves that allowed vacuum to reach the forge DV causing rattling instead of the ECU?


Anything is possible, though i think it was fine. The car was only three years old when i got rid of the system (now it will be 12 in february). It has been chipped (almost) from day one, used forge DV for some years, then put a plastic 710N in it. Long term reliabilty issues can be ruled out for sure! 

EDIT: Still using the first K03 turbo of course.


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## Sim (Jun 27, 2002)

elRey said:


> But I don't want to win simply by the other side getting tired and giving up.


I will make my logs next week (to TRY) to prove that manifold vacuum is adequate to opeate the DV (therefore no N249 is needed for this purpose).


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## elRey (May 15, 2001)

Not completely empirical data (lack of log data), but someone's experience ....
http://www.youtube.com/watch?v=1vaRDFEKCjA

And this one, IMO, would suggest N249 opens DV when there's more pressure in charge pipe. i.e. sooner.
http://www.youtube.com/watch?v=ZA1iXEMN6j8


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## Sim (Jun 27, 2002)

elRey said:


> And this one, IMO, would suggest N249 opens DV when there's more pressure in charge pipe. i.e. sooner.
> http://www.youtube.com/watch?v=ZA1iXEMN6j8


They do sound different, for sure. I agree (and that was not a question at all), that if driver lets off throttle lets say from 100% to 20-25% (only) and there is no poweful vacuum in the manifold, but increased pressure in the charge pipe, the n249 can open the DV (sooner). This however fits the "theory" of N249 limiting pressure in part throttle applications me and some other members were talking about.

BTW: I can hear slight fluttering in both cases.

EDIT: Watched it again and he drives the no n249 version a lot more "spirited", no wonder the valve is louder.


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## elRey (May 15, 2001)

Sim said:


> This however fits the "theory" of N249 limiting pressure in part throttle applications me and some other members were talking about.


Sorry I did get off the current discussion with those videos. What you said here is what we are focusing on.

I can log ECU's signal to DV. How can I drive to show this is true or not? I don't want to waste a logging session only to find out I never put the car into the situation in question. I'm reluctant to offer logging data as it maybe perceive as biased.




Sim said:


> EDIT: Watched it again and he drives the no n249 version a lot more "spirited", no wonder the valve is louder.


I'd like to come back to this later.


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## Sim (Jun 27, 2002)

elRey said:


> Sorry I did get off the current discussion with those videos. What you said here is what we are focusing on.
> 
> I can log ECU's signal to DV. How can I drive to show this is true or not? I don't want to waste a logging session only to find out I never put the car into the situation in question. I'm reluctant to offer logging data as it maybe perceive as biased.


I would use a bone stock software (on a stock car which is hard to find). I would crank up the boost with an MBC for example (well over requested), and log what happens.


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## elRey (May 15, 2001)

Sim said:


> I would use a bone stock software (on a stock car which is hard to find). I would crank up the boost with an MBC for example (well over requested), and log what happens.


Hmmm, then I'm out. I don't have any cars that match those requirements.


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## Sim (Jun 27, 2002)

elRey said:


> Hmmm, then I'm out. I don't have any cars that match those requirements.


Me neither.

EDIT: But have a guess what may happen .


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## clrwatrtom (Jan 31, 2013)

*is there no one willing to address my question?*



clrwatrtom said:


> Good morning, i have to admit that most of what i have read in this thread is beyond my ability to understand, but if i have hurt my fuel economy by deleting the N249, i would like to get it back.
> I have an 03TT coupe 180FWD that has a 3"DP and hiflow cat with a 2 1/2" exhaust with a turbo muffler, a silicone TIP, Newsouth performance intake manifold gasket, adjustable spring pressure DV, alloy catch can, SAI Delete and EVAP Delete. If i were to re-install my Vacuum reservoir and N249, how would i tie it into my existing setup? Are there any diagrams that would show me how to connect the N249 and reservoir to my current setup?
> I appreciate any help one or all may have and hats off to you folks that have contributed to this thread as although i am still overwhelmed and confused, am am better educated about this topic than i was before reading this thread.
> Thanks, tom


Good morning.
After reading this thread i realize i might have been premature in deleting my N249. I would like to re-install it while keeping my catch can intact as i found a good bit of oil in my intercooler. Does anyone have a solution to my dilemma?


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## BW-Boosted (Jan 3, 2014)

So, here are my experiences. Last year i did some dyno tests and had some issues with boost stability. So i decided to replace the N249 by a hose. But now i have a massive surge issue while shifting over 1,5bar (22psi). I'm going to reinstall it.

(sorry for bad english)


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## Slimjimmn (Apr 8, 2006)

N249 does absolutely nothing for boost stability 
It only serves 2 purposes
-open the diverter valve for normal operation
-open the dv to limit boost or engine protection

That is all
It's not there to give some special "drivability" fix
Open dv
Limit boost

Done
>thread


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## BW-Boosted (Jan 3, 2014)

Yes, i know. I tought, that there was a leakage, so i wanted to try some tests without the n249.


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## elRey (May 15, 2001)

Slimjimmn said:


> N249 does absolutely nothing for boost stability
> It only serves 2 purposes
> -open the diverter valve *to enhance normal operation for better respool*
> -open the dv to limit boost or engine protection* <- incorrect, or at least currently being debated*
> ...


Some comments ^

So, not done and not end of thread.


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## elRey (May 15, 2001)

Sim, is this you back in 2004? -> http://www.seatcupra.net/forums/showthread.php?t=42406


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## [email protected] Performance (Sep 17, 2013)

Holy investigative research elRey! :laugh::beer:


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## Budsdubbin (Jul 14, 2008)

Holy hell you guys fired up a topic from 2005. So your fighting over the function of a solenoid & mechanism that literally reacts in milliseconds regardless of the n249 system. I find it hard to fathom the stock reservoir would have the capacity to supply enough vacuum to crack or open say a Tial qr sized dv before manifold vaccum. Although I'm sure stock-like dv setup's would benefit but from this end it's nitpicking.


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## DMVDUB (Jan 11, 2010)

Wait a minute here...

The N249 DOES open the DV when the ECU freaks out to reduce boost. :sly:

Also I'd like to know why removing the N249 IMPROVES drivability in almost (if not ) every 1.8t I've seen.


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## elRey (May 15, 2001)

DMVDUB said:


> The N249 DOES open the DV when the ECU freaks out to reduce boost. :sly:


Everyone keeps repeating this protective, fail-safe function, but no one has provided evidence of it. ME7 Doc and ME7 code says otherwise. Show me one single log of N249 activation without overrun on a 1.8T.



DMVDUB said:


> Also I'd like to know why removing the N249 IMPROVES drivability in almost (if not ) every 1.8t I've seen.


Not every, but I can't argue that vast majority report positive results. However, I could offer a plausible reason. Question is whether you would just shrug it off as a closed mind grasp on my part.


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## DMVDUB (Jan 11, 2010)

elRey said:


> Everyone keeps repeating this protective, fail-safe function, but no one has provided evidence of it. ME7 Doc and ME7 code says otherwise. Show me one single log of N249 activation without overrun on a 1.8T.
> 
> 
> 
> Not every, but I can't argue that vast majority report positive results. However, I could offer a plausible reason. Question is whether you would just shrug it off as a closed mind grasp on my part.


I asked what you thought. I don't "shrug" things off if people are giving a well thought out explanation and they remain respectful. I have a feeling you're thinking of my temper with people when you say that. I treat people the way they treat me. So give me your idea, because I don't really know why they seem to work better without it. 

Also, there is documentation about it. Give me some time to go through my info and I'll find it. I've got 10,000+ pages of tuning info about this ECU alone :banghead:


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## turbo2.24.1990 (Jun 2, 2008)

Budsdubbin said:


> I find it hard to fathom the stock reservoir would have the capacity to supply enough vacuum to crack or open say a Tial qr sized dv before manifold vaccum. Although I'm sure stock-like dv setup's would benefit but from this end it's nitpicking.


As groggory mentioned earlier, I'd be really interested in finding out exactly why the n249 system doesn't like aftermarket dv's. Yeah it's nitpicking, but it'd be nice to be able to use the really nice aftermarket dv's that hold up to high boost applications with the n249. I've been thinking about how you could modify the vacuum reservoir to work with stiffer dv's-how could we increase the amount of vacuum it holds? I thought about making it bigger, but that reminds me of people putting bigger brake booster reservoirs on their cars-it doesn't increase the amount of vacuum force, but rather increases the number of power assisted stops you can have with the engine not supplying vacuum in emergency situations.


elRey said:


> Not every, but I can't argue that vast majority report positive results. However, I could offer a plausible reason. Question is whether you would just shrug it off as a closed mind grasp on my part.


^^This. I think it's just easier for everyone that wants to use a stronger aftermarket dv to delete the system and call it good. The n249 delete has the record of success that it does simply because people haven't taken the time for whatever reason to figure out how to make the n249 work with the aftermarket dv's. I want to come up with solutions for this, specifically talking about vacuum reservoir capabilities and see this discussion go further in that direction.


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## DMVDUB (Jan 11, 2010)

I'm not searching though all my crap so I'll give you this,

They explain how the DV is used for Overboost protection and the there's maps related.

http://nefariousmotorsports.com/forum/index.php?topic=950.0


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## [email protected] Performance (Jul 20, 2011)

I'll add a little twist to this thread since my curiosity has now been piqued:

Has anybody proved that a brand new stock DV cannot hold 23psi?

They also have the upgraded unit that is fitted on Porsche vehicles which we can use if indeed that's the case.


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## DMVDUB (Jan 11, 2010)

[email protected] Performance said:


> I'll add a little twist to this thread since my curiosity has now been piqued:
> 
> Has anybody proved that a brand new stock DV cannot hold 23psi?
> 
> They also have the upgraded unit that is fitted on Porsche vehicles which we can use if indeed that's the case.


A stock DV 710N will hold 23psi just fine. We've got it holding 25-28psi on my friend Carls GLI. As long as a K03S can hold it that is :laugh:


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## elRey (May 15, 2001)

DMVDUB said:


> I asked what you thought. I don't "shrug" things off if people are giving a well thought out explanation and they remain respectful. I have a feeling you're thinking of my temper with people when you say that. I treat people the way they treat me. So give me your idea, because I don't really know why they seem to work better without it.
> 
> Also, there is documentation about it. Give me some time to go through my info and I'll find it. I've got 10,000+ pages of tuning info about this ECU alone :banghead:



Sorry. I'd love to see what you dig up. 

As for possible reason why some might have a positive result after the bypass... A weak vacuum source would cause a weak and/or delayed DV opening. If the there was any small leak in any of the N112 or N249 hoses it would cause the stored vacuum in reservoir to leak out or never accumulate to begin with. And when manifold vacuum would open DV normally, that same leak would weaken the vacuum signal to DV. Bypass a faulty, even slightly faulty, N112/N249 system you revitalize DV operation. 

And for what ppl think is N249 opening DV during acceleration causing surging... If vacuum reservoir is storing vacuum properly and hoses are all good, and N249 valve itself is faulty and allows a small leak to the reservoir, even when not activated, then the slight vacuum on DV and high pressure in charge pipe might cause false opening of DV.


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## [email protected] Performance (Jul 20, 2011)

DMVDUB said:


> A stock DV 710N will hold 23psi just fine. We've got it holding 25-28psi on my friend Carls GLI. As long as a K03S can hold it that is :laugh:


That's what I thought


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## elRey (May 15, 2001)

DMVDUB said:


> I'm not searching though all my crap so I'll give you this,
> 
> They explain how the DV is used for Overboost protection and the there's maps related.
> 
> http://nefariousmotorsports.com/forum/index.php?topic=950.0


Reading...


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## DMVDUB (Jan 11, 2010)

elRey said:


> Sorry. I'd love to see what you dig up.
> 
> As for possible reason why some might have a positive result after the bypass... A weak vacuum source would cause a weak and/or delayed DV opening. If the there was any small leak in any of the N112 or N249 hoses it would cause the stored vacuum in reservoir to leak out or never accumulate to begin with. And when manifold vacuum would open DV normally, that same leak would weaken the vacuum signal to DV. Bypass a faulty, even slightly faulty, N112/N249 system you revitalize DV operation.
> 
> And for what ppl think is N249 opening DV during acceleration causing surging... If vacuum reservoir is stored vacuum properly and hoses are all goodd, N249 valve itself is fault and allow a small leak to reservoir even when no activated, then the slight vacuum on DV and high pressure in charge pipe might cause false opening of DV.


I think you have a very good idea here and it's a sound one as well. It could very well be a cause of some peoples problems. :thumb up:

About it opening during Accel causing surging, you're right. It is either open or it's closed. There's no kinda open. 

But, here's my theory on that; when the ecu is not properly set to ignore over boost or over boost is set too low the N249 (first action by the ecu for self preservation) will bleed boost down to where it's "safe" zone is. When boost goes back up it does it again. The best way to see this in action would be to have someone with a N249 and surge connect a test light to the N249 so we can see when it's activating in real time. 

The ECU has a few ways to "preserve" itself, it can blow off boost, it can cut timing, it can cut fuel and it can slam the throttle plate shut. These are the most common and extreme methods you'll see. Me for example, my car has no N249 and if it's mad at me about something it limits how far the throttle will open. I can't remember the last time it happened but it was easy to see in logs.

*Throttle cut*
_If you don't get all of this just right, and your actual boost goes too far above requested boost (by ~200mBar), you may experience overboost throttle cut due to negative deviation, which is ME attempting to get boost back under control by temporarily closing the throttle plate.
Positive deviation
Alternately, if your requested boost is far too high for a given load/rpm point, you may experience positive deviation (underboost) limp mode. This occurs if actual boost is too far under requested boost for too long. The result will be the P1557 Positive Deviation code, and from then on out, WGDC restricted to 10%.
If your MAF scaling is too aggressive, your load may be reading high, which might enable positive deviation diagnosis too early during a pull. Fix this by scaling back MLHFM
If your requested boost ramp is too aggressive for your turbos, you may be requesting far more boost than your turbo can possibly make at low rpms. In particular, the stock K03 LDRXN is VERY aggressive. K04s (let alone bigger turbos) will never spool that fast. Make sure LDRXN does not allow too much spec load too soon!
If none of the above helps, consider tweaking NDLDRAPU and SDLDRA.
If you are running K04s, you probably want to use the RS4 maps for all of these areas as a starting point, rather than the stock K03 maps._


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## turbo2.24.1990 (Jun 2, 2008)

DMVDUB said:


> A stock DV 710N will hold 23psi just fine. We've got it holding 25-28psi on my friend Carls GLI.


I think that the general consensus is that stock dv's will hold relatively high boost levels just fine, but not for very long. How long has that 710N been in use?


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## DMVDUB (Jan 11, 2010)

turbo2.24.1990 said:


> I think that the general consensus is that stock dv's will hold relatively high boost levels just fine, but not for very long. How long has that 710N been in use?


How long? don't know. Lot's of other custom NA to FI setups will use the 710N in favor of a BOV because of the responsiveness, at the same time a lot of the people going FI want that damned BOV sound more than the power. :banghead:


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## elRey (May 15, 2001)

DMVDUB said:


> But, here's my theory on that; when the ecu is not properly set to ignore over boost or over boost is set too low the N249 (first action by the ecu for self preservation) will bleed boost down to where it's "safe" zone is. When boost goes back up it does it again. The best way to see this in action would be to have someone with a N249 and surge connect a test light to the N249 so we can see when it's activating in real time.
> 
> The ECU has a few ways to "preserve" itself, it can blow off boost, it can cut timing, it can cut fuel and it can slam the throttle plate shut. These are the most common and extreme methods you'll see. Me for example, my car has no N249 and if it's mad at me about something it limits how far the throttle will open. I can't remember the last time it happened but it was easy to see in logs.
> 
> ...


I finished the nefmoto thread. There was no documented support for N249 protection function, only the same word of mouth. Neither is there any in the text you quoted.

I did see this (still not documented by poster):


> Apparently I have a regulated BOV that just brings the boost down evenly *when calculated load goes* down.


By simply forcing throttle cut, the DV will open anyway. ME7 does not use the N249 for protection.

And there is a variable that can be, has been logged for N249 activation.


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## DMVDUB (Jan 11, 2010)

http://audi.service-bg.com/Articles/usermanuals/Audi-A4_A6_A8/1.8T%20Troubleshooting%20Guide.pdf

Limp Mode – These cars are designed to protect themselves from engine damage. If the engine boosts too much, or the engine does not get enough fuel it will go into a limp mode where boost is limited to protect the engine.* It limits boost by controlling a solenoid on the wastegate line (N75), by closing the electronic throttle or by opening the DV valve.* If you are experiencing a limp mode the best thing to do is get the car scanned for codes and to see what is wrong. Look at fuel trims for signs of running lean, and to look for MAF problems, or O2 sensor problems. To look for potential boost problems log Block 115 and you can see the specified Vs actual boost. If you exceed the specified then there is a good chance that you will go into this limp mode. Stock specified is a max of 14 psi for a 2002+ car.

As stated in bold, by closing the electronic throttle OR opening the DV (there's only one way it's opening the DV that is different than closing the throttle plate  )


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## elRey (May 15, 2001)

DMVDUB said:


> http://audi.service-bg.com/Articles/usermanuals/Audi-A4_A6_A8/1.8T%20Troubleshooting%20Guide.pdf
> 
> Limp Mode – These cars are designed to protect themselves from engine damage. If the engine boosts too much, or the engine does not get enough fuel it will go into a limp mode where boost is limited to protect the engine.* It limits boost by controlling a solenoid on the wastegate line (N75), by closing the electronic throttle or by opening the DV valve.* If you are experiencing a limp mode the best thing to do is get the car scanned for codes and to see what is wrong. Look at fuel trims for signs of running lean, and to look for MAF problems, or O2 sensor problems. To look for potential boost problems log Block 115 and you can see the specified Vs actual boost. If you exceed the specified then there is a good chance that you will go into this limp mode. Stock specified is a max of 14 psi for a 2002+ car.
> 
> As stated in bold, by closing the electronic throttle OR opening the DV (there's only one way it's opening the DV that is different than closing the throttle plate  )


 check the author :thumbup: more word of mouth. Unless, of course, Bosch and VAG make a habit of referencing Ross-Tech and APR for their tech documents. :laugh:


Edit: checked it for you: http://www.elitedubs.com/index.php?topic=988.0
He's a vortex user :beer:


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## [email protected] Performance (Jul 20, 2011)

Over boost condition is almost always followed by either throttle cut or limp mode. When there is throttle intervention of course the N249 will do its thing.

I think elRey is right here (as usual).


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## elRey (May 15, 2001)

[email protected] Performance said:


> Over boost condition is almost always followed by either throttle cut or limp mode. When there is throttle intervention of course the *DV* will do its thing.
> 
> I think elRey is right here (as usual).


Small edit ^. And the 'as usual' wasn't necessary..... But I'll take it  until the next time I'm not :laugh:

Joking aside, I understand if I am right, it's only about this small part of the current discussion.... when does the ECU use the N249 and when does it not. Which is a small part in itself of the bigger discussion... N249 PROs/CONs.


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## Sim (Jun 27, 2002)

elRey said:


> Sim, is this you back in 2004? -> http://www.seatcupra.net/forums/showthread.php?t=42406


Yes, that was me.
EDIT: You are really obsessed


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## Sim (Jun 27, 2002)

elRey said:


> Everyone keeps repeating this protective, fail-safe function, but no one has provided evidence of it. ME7 Doc and ME7 code says otherwise. Show me one single log of N249 activation without overrun on a 1.8T.


I wont start over, just a thought (no proof or anyhing at all, just my "common sense").

If you were an engineer at a big factory where they are designing cars to be manufactured in millions of pieces and you were told to protect the engine from fatal failures (because failing engines would yield some bad reputation for sure) and you already had the N249 on the top of the engine (for any other possible reason), would you just MISS using it as a very easy and effective way to prevent overboosting? Using it is just as easy as flipping a bit in a variable ("hello world" applications use to be this complicated  ). $0.02


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## elRey (May 15, 2001)

Sim said:


> I wont start over, just a thought (no proof or anyhing at all, just my *"common sense"*).
> 
> ....


I agreed. It is very logical. Which is why I think everyone *assumes* it's a function of the N249. But as they say "proof of the pudding is in the eating".





[email protected] Performance said:


> Holy investigative research elRey! :laugh::beer:





Sim said:


> Yes, that was me.
> EDIT: You are really obsessed


When I start a fight, I like to know my opponent. So, afterwards, if I lose, I know where he lives and who his loved ones are.........
Or if I can't discredit someone's argument, I dig up dirt on the person and discredit them!



:laugh: Just kidding. His thread was referenced in several other N249 related threads that I came across. :beer:


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## [email protected] Performance (Jul 20, 2011)

Sim said:


> I wont start over, just a thought (no proof or anyhing at all, just my "common sense").
> 
> If you were an engineer at a big factory where they are designing cars to be manufactured in millions of pieces and you were told to protect the engine from fatal failures (because failing engines would yield some bad reputation for sure) and you already had the N249 on the top of the engine (for any other possible reason), would you just MISS using it as a very easy and effective way to prevent overboosting? Using it is just as easy as flipping a bit in a variable ("hello world" applications use to be this complicated  ). $0.02


Wastegate crack pressure is 5psi. 180hp cars run about 11psi stock. I don't see how a catastrophic overboost would happen. And even if overboost happens, the ECU can close the TB and trigger limp mode almost instantly.

Most of the times its the other way around, underboost happens due to leaks or tired hardware.


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## [email protected] Performance (Jul 20, 2011)

elRey said:


> Small edit ^. And the 'as usual' wasn't necessary..... But I'll take it  until the next time I'm not :laugh:
> 
> Joking aside, I understand if I am right, it's only about this small part of the current discussion.... when does the ECU use the N249 and when does it not. Which is a small part in itself of the bigger discussion... N249 PROs/CONs.


Yes but for about 3 pages a discussion broke out about the N249 being used for overboost. I don't think anyone has ever shown any proof of this yet you were taking a beating out here.


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## elRey (May 15, 2001)

Someone made a good point in another thread that if the ECU used the N249 in an overboost fail-safe BEFORE cutting throttle, it would cause the turbo shaft to over spin. The throttle open and no load on compressor != turbo protection.


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## Sim (Jun 27, 2002)

elRey said:


> :laugh: Just kidding. His thread was referenced in several other N249 related threads that I came across. :beer:


Back in 2004 (and the past years, when i begun tampering with my and my mates car) there wasn't any (useful) info in this depth available to the public regarding to ME7 (even damos files were big treasures). Unless you bought a tuning package (for an arm and leg) you had no choice to do mods to the ECU by yourself. In 2002 i went to the most trusted tuner here who could not make the car go/work the way i wanted, so i decided to do everything on my own. Before i would be able to hack into the ecu I did lots of experimenting with N75 restrictors, different MBC setups, etc. I have learned there, that you cannot just trurn up the boost, if ECU wants it will release boost. Later in 2005/6 i did my own (quite basic) tuning software for the ME7 (remember, no me7 docs were available), i even got a little help from Andy Whittaker regarding to a checksum which i could not find (bummer). My tuning software and its abilities weren't competitive with the "pro" tuning suites so i finally abandoned the project. In 2009 i have decided to do my own ECU (absolutely just for fun) which is working for now almost two years ago, i am using it in my and my mates cars.


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## Sim (Jun 27, 2002)

elRey said:


> Someone made a good point in another thread that if the ECU used the N249 in an overboost fail-safe BEFORE cutting throttle, it would cause the turbo shaft to over spin. The throttle open and no load on compressor != turbo protection.


Sounds reasonable. If DV would shut close back as pressures are safe again, this would not eliminate all load on the compressor.


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## elRey (May 15, 2001)

Just to reel everyone back in from the rabbit hole we went down the last few pages:


_work in progress_

*PROs**CONs*

*Improved respool after shifts* - to be debated around is there enough time between TB closing and vacuum building in IM for N249 to have any real affect

*Better MPG* - yet to discuss



*Complexity prone to faulty vac leaks,etc * - uncontested

*Cleaner bay* - uncontested

*Solenoid/long hoses introduce restriction causing weak signal* - partially debated



Fail-safe device - found to be not true in discussion on when N249 is activated and when it is not



N249 opens during acceleration causing boost instability - found to be not true in discussion on when N249 is activated and when it is not




[tr]


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## Slimjimmn (Apr 8, 2006)

DMVDUB said:


> I'm not searching though all my crap so I'll give you this,
> 
> They explain how the DV is used for Overboost protection and the there's maps related.
> 
> http://nefariousmotorsports.com/forum/index.php?topic=950.0


To add to this, in the oem parts catalog the diverter valve (as everyone calls it) is actually ethnically translated from German to English as the "overrun cutoff valve" hence its use for over boost protection.


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## elRey (May 15, 2001)

Slimjimmn said:


> To add to this, in the oem parts catalog the diverter valve (as everyone calls it) is actually ethnically translated from German to English as the "overrun cutoff valve" hence its use for over boost protection.


I have a suspicion you're trying to be funny, but I'll bite. 
Is the part called the same for the AEB? If so, how could it be named for a founction the AEB didn't have the ability to deploy since it didn't have a N249?

There are several points that could be brought up against you logic. That's just the most simple one.


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## Sim (Jun 27, 2002)

I could do this log today (K03, no N249, DV=710N, 50 samples per second). I tapped the DV control line with a T and put a pressure sensor there. I still need a MAF to check if there is a compressor surge (i am running mafless at the moment).

The closing speed of the throttle body is around 120ms (from 100% to lets say to 5%), but it also depends on how quick do you let off your foot off the pedal. The pressure in the charge pipe begins to rise a little bit sooner (as the TB does not have to be completely closed to act as a severe restriction). At this point (where pressure spike begins to build up) there is no vaccum in the DV control line, though the pressure difference is already significant (0.5bar). The pressure is increasing for ~60ms and then tapers off. When pressure increase stops (at 223kPa) , the DV control pressure is 101kPa (maybe this difference is enough for the DV to open).










Is the pressure spike dangerous or would it stall compressor significantly? (base pressure was 190kPa)
Can the N249 be fast enough to counter act pressure spike? (if it checks for positive pressure deviation, i think it is already too late).


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## rstolz (Jun 16, 2009)

> By open-loop, do you mean boost control or lambda control?


sorry, been away a couple days. Cool stuff happening here. Anyway, I meant boost control, lambda would be closed loop.

it's not terribly relevant to the current discussion trend, but:

Any DV opening event triggered by the N249 could only be momentary, the vacuum reservoir isn't large enough to provide enough sustained vacuum to hold it open, or open it repeatedly, without replenishing the vacuum.

like trying to use an air powered cutting wheel or paint sprayer off of a 1-gallon air tank.

which, now that i think of it, might be a contributor to fluttering DV. If the N249 is trying to "hold open" the DV, it may only succeed by fluttering it. or your vacuum canister/check valve is compromised.

also a very nice diagram to add some color:
http://shaw-clan.com/beetlepix/N249cutaway.pdf


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## Slimjimmn (Apr 8, 2006)

elRey said:


> If so, how could it be named for a founction the AEB didn't have the ability to deploy since it didn't have a N249? .


I'm not sure of the parts catalog name for aeb engine code. I guess someone could check. 
On a side note, maybe the engineers realized they could use the dv for additional safety device after the aeb engine when the n75 failed so they invented the n249. 
Also the aeb used straight to intake for more natural boost actuation when letting off the gas


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## BW-Boosted (Jan 3, 2014)

Sorry for my bad english, I try to find the best words.
Your issue is exactly what I wrote in my post a couple days ago. Without the N249 you have surging problems. 
I have logged the same on my engine when I close the throttel.

What happens? Depending on decrasing volume flow the compressor power goes down. The outlet pressure is a function based on shaft speed an mass flow. Because the flow is zero (trottle is closed) the speed is incrasing --> boost goes up. in my case there is not enough vacuum to open the Recirulation valve for a long time. 

And yes, this is dangerous because the trust load is reversing to the other side and "hits" the trust bearing. You must be carefull doing this for a long time.

Last but not least, here is my log with 150Hz 
The upper red line shows the pressure, measured DIRECTLY after compressor outlet.
The blue line below shows the pressure in the intakte manifold


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## Sim (Jun 27, 2002)

rstolz said:


> Any DV opening event triggered by the N249 could only be momentary, the vacuum reservoir isn't large enough to provide enough sustained vacuum to hold it open, or open it repeatedly, without replenishing the vacuum.


Welcome back! 
You are right about the limited vacuum storage capacity of the reservoir. I have no idea how many times can it open the DV before running out of vacuum, BUT once the DV is opened and there is no air leaks in the system it can hold it open until N249 is opening back.


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## Sim (Jun 27, 2002)

BW-Boosted said:


> The upper red line shows the pressure, measured DIRECTLY after compressor outlet.
> The blue line below shows the pressure in the intakte manifold


Cool log! However, the graphs are not inline with each other and that may be a bit misleading. Zooming in would also help a lot!


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## groggory (Apr 21, 2003)

Sim said:


> Cool log! However, the graphs are not inline with each other and that may be a bit misleading. Zooming in would also help a lot!


The logs are not in line with each other and the scaling factor of the x axis of the two graphs are different too.

I had some fun with mspaint and brought the x and y scales in line and factor


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## BW-Boosted (Jan 3, 2014)

Sim said:


> Cool log! However, the graphs are not inline with each other and that may be a bit misleading. Zooming in would also help a lot!


What do you mean with "they are not inline"? Do you want a log with a overlay? This is no problem.
Here is another view of this log. 

An overview of the test log. 3rd - 4th - 5th gear. pedal to the medal on the highway 
Red line presure in the stainless steel pipe conected to the compressor outlet (only positiv pressure possible)
Blue line pressure in the intake manifold.
Difference between the line is depending on pressure losses in the intercooler (OEM)

The SAME scale at y-axis (!)
y-axis is mbar











Zoomed in while shifting.


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## Sim (Jun 27, 2002)

groggory said:


> I had some fun with mspaint and brought the x and y scales in line and factor


A lot better! Can you zoom in, too?


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## Sim (Jun 27, 2002)

BW-Boosted said:


> What do you mean with "they are not inline"? Do you want a log with a overlay? This is no problem.
> Here is another view of this log.
> 
> A overview of the test log. 3rd - 4th - 5th gear. pedal to the medal on the highway
> ...


Cool, thanks! I (we) would like to know the duration of these spikes.

It is not a question that these spikes can get developed, the question is if they do hurt performance or not.
I do not think that these would hurt the turbo at all, as these spikes are very short in time and hundreds (thousands) of people (including me) are running their cars with no249 for long years (+ how about all the cars which have been sold without this solenoid at all?).

***

My opinion is that N249 could prevent these spikes, if it checked the pressure in the intercooler versus the TPS (as i already described).


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## groggory (Apr 21, 2003)

Sim said:


> My opinion is that N249 could prevent these spikes, if it checked the pressure in the intercooler versus the TPS (as i already described).


x2

Essentially, the IDEA of the N249 seems like a good one. However, the software would have to take advantage of it and we would likely need to beef up the N249 system to handle more demanding aftermarket diverter valves.

Perhaps a larger orifice version of the N249 so we were running 1/4" ID hose throughout the entire N249 pneumatic circuit. Perhaps a repurposed electronic boost control solenoid could work for this situation.

....I'm perfectly happy with my bypassed N249 setup on my GT2871r + Forge 007 setup. Just saying that the N249 idea is a cool one if it is tackled properly.


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## BW-Boosted (Jan 3, 2014)

Sim said:


> Cool, thanks! I (we) would like to know the duration of these spikes.
> 
> It is not a question that these spikes can get developed, the question is if they do hurt performance or not.
> I do not think that these would hurt the turbo at all, as these spikes are very short in time and hundreds (thousands) of people (including me) are running their cars with no249 for long years (+ how about all the cars which have been sold without this solenoid at all?).
> ...




I'm not sure. With the raw data i can only "see" a duration of 50-100ms, because this was a long term run with a lower sampling rate. I have to to this test again with more samles. Possible is nearly 1000 samples (1kHz) per second per chanel :thumbup:

My point is:
Yes, in my case it is dangerous. At first you can hear it while shifting. The typical "tsch tsch tsch" 
Another point is, that I'm running a small thrust bearing to reduce powerloss and get a higher boost pressure. As you can see, I'm running this K04-023 with nearly 2bar (Overboost) and 1,4bar at full engine speed.

I'm going to reinstall the N249 and will whink about another and better solution.


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## Sim (Jun 27, 2002)

groggory said:


> Just saying that the N249 idea is a cool one if it is tackled properly.


Agreed. Sadly it has its side effects, too (some are debated).
I am totally comfortable without it and i am not concerned about the problems which may arise without one!


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## Sim (Jun 27, 2002)

BW-Boosted said:


> I'm going to reinstall the N249 and will whink about another and better solution.


We would be glad to see these logs with the N249 installed.
Any chance to log TPS and N249 signal, too?


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## Sim (Jun 27, 2002)

BW-Boosted said:


> Yes, in my case it is dangerous. At first you can hear it while shifting. The typical "tsch tsch tsch"


Maybe you already exceeded the flow capabilities of the DV.


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## BW-Boosted (Jan 3, 2014)

Sim said:


> We would be glad to see these logs with the N249 installed.
> Any chance to log TPS and N249 signal, too?


I will do these tests in march or april - after winter 
unfortunately this is not possible with the actual equipemnt. I installed a quad pressure messurement to get values from
-Ambient
-vacuum in the air filter (this is very much!!!)
-pressure after compressor
-pressure manifold

Perhaps i will exapand the system or replace two pressure sensors



Sim said:


> Maybe you already exceeded the flow capabilities of the DV.


I dont think so, because first test with the N249 you cant here the noise
And the flow isn't that high. Only 420Nm with a little bit more than 280Hp


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## elRey (May 15, 2001)

rstolz said:


> Now a question, since you can clearly read the code easily:
> At WOT you're in open-loop, does open-loop *boost control* affect the operation of the N249? Or does it operate the same whether in closed or open loop?


The function that operates the N249 does not reference whether in closed or open loop boost control. So, the way I read it, the N249 will operate as usually while in open-loop.


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## elRey (May 15, 2001)

Sim said:


> I could do this log today (K03, no N249, DV=710N, 50 samples per second). I tapped the DV control line with a T and put a pressure sensor there. I still need a MAF to check if there is a compressor surge (i am running mafless at the moment).
> 
> The closing speed of the throttle body is around 120ms (from 100% to lets say to 5%), but it also depends on how quick do you let off your foot off the pedal. The pressure in the charge pipe begins to rise a little bit sooner (as the TB does not have to be completely closed to act as a severe restriction). At this point (where pressure spike begins to build up) there is no vaccum in the DV control line, though the pressure difference is already significant (0.5bar). The pressure is increasing for ~60ms and then tapers off. When pressure increase stops (at 223kPa) , the DV control pressure is 101kPa (maybe this difference is enough for the DV to open).
> 
> ...


Great logs.

So, DV pressure would be the same as manifold pressure (post-TB), right? And your Manifold Absolute Pressure sensor is the MAP (pre-TB), right?


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## Sim (Jun 27, 2002)

elRey said:


> So, DV pressure would be the same as manifold pressure (post-TB), right? And your Manifold Absolute Pressure sensor is the MAP (pre-TB), right?


Yes it is misleading. The Manifold Absolute Pressure is the Intercooler pressure, and the DV pressure is the "real" manifold absolute pressure. But this is how ME7 is hooked up.


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## BW-Boosted (Jan 3, 2014)

While analysing the data I saw another interesting fact what happens with the pressure at compressor INLET. If you want i can make another preparation of the log where you can see that the turbo is hard surging!



> The Manifold Absolute Pressure is the Intercooler pressure


i guess you mean the pressure before intercooler?
In my case i have a pressure loss of 0,3bar (~4psi) at the intercooler


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## Sim (Jun 27, 2002)

BW-Boosted said:


> While analysing the data I saw another interesting fact what happens with the pressure at compressor INLET. If you want i can make another preparation of the log where you can see that the turbo is hard surging!


Of course! If you say you can hear the fluttering sound it must be surging for sure!



BW-Boosted said:


> i guess you mean the pressure before intercooler?


I mean the stock MAP location. In my car it is in the charge pipe between the IC and throttle body (so basically it is after the IC).


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## elRey (May 15, 2001)

Sim said:


> (if it checks for positive pressure deviation, i think it is already too late).


I not only looks are actual, but requested as well. So, even if actual was falling, if it wasn't falling as fast as requested, it would still activate N249. Even if there was no change in actual, but requested fell (as it does when letting off gas), the function see that change and opens DV.
Looking back at my previous attempts to explain the conditions under which the N249 is opened are all incomplete to some degree.




elRey said:


> More specifically it takes the change in actual pressure (slope), multiples it by 3, then compares that exaggerated delta to a threshold map. Input to the map are RPM and requested pressure.
> So, if actual pressure change (current pressure - previous read pressure) * 3 > 200hPa AND negative pedal gradient = open DV. So, it actual doesn't HAVE TO cross requested. It was just easier to state it that way. So, more correct generalization would be to say if actual pressure rises/changes too much + pedal back off = open DV.



Where I mention actual pressure it's really actual - requested. 

(current pressure - previous read pressure) * 3 > 200hPa

should read

(current [actual pressure - requested pressure] - previous read [actual pressure - requested pressure]) * 3 > 200hPa

So, if you leave actual pressure constant, just the fact that requested is changing (falling), it's enough for ECU to open DV.




Sim said:


> The closing speed of the throttle body is around *120ms* (from 100% to lets say to 5%), but it also depends on how quick do you let off your foot off the pedal. The pressure in the charge pipe begins to rise a little bit sooner (as the TB does not have to be completely closed to act as a severe restriction). At this point (where pressure spike begins to build up) there is no vaccum in the DV control line, though the pressure difference is already significant (0.5bar). The pressure is increasing for *~60ms* and then tapers off. When pressure increase stops (at 223kPa) , the DV control pressure is 101kPa (maybe this difference is enough for the DV to open).



Thanks for quantifying *INSTANTLY* :beer:


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## Sim (Jun 27, 2002)

Can decreasing requested pressure trigger N249?


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## rstolz (Jun 16, 2009)

> The function that operates the N249 does not reference whether in closed or open loop boost control. So, the way I read it, the N249 will operate as usually while in open-loop.


cool:thumbup:


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## Sim (Jun 27, 2002)

elRey said:


> Thanks for quantifying *INSTANTLY* :beer:


Ah, cmon! We all know things dont happen by the speed of light. :laugh:
FYI: My DV is fed by ca a one meter long (overall) 4mm ID silicon hose, and 2 T-s (3mm id) in it (1 for F PR and 1 for the pressure sensor).


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## elRey (May 15, 2001)

Sim said:


> Can decreasing requested pressure trigger N249?


With a negative pedal gradient, yes.


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## Sim (Jun 27, 2002)

elRey said:


> With a negative pedal gradient, yes.


Are you sure that without it wont?


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## elRey (May 15, 2001)

Sim said:


> Are you sure that without it wont?


Yes.

ME7 Documentation of N249 control:









Keep in mind, the cruise function that *Chickenman35 * mentioned is controlled by the map SVDLDUVS which is zeroed out on 1.8T applications.


plsol_w = requested boost
pvdkds_w = actual boost
wped = pedal position
nmot = RPM
dwped = pedal gradient
pu_w = ambient pressure
B_ll = idle condition

GWPLDU = -1.953%
SDKSUA = all 100%
KFSDLDSUA = mostly 200hPa


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## Sim (Jun 27, 2002)

Thanks, but thats too much . I will try my stock me7 with an MBC next week.


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## groggory (Apr 21, 2003)

ElRey,

Would you be willing to go through that diagram and teach us how to read it?


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## elRey (May 15, 2001)

groggory said:


> ElRey,
> 
> Would you be willing to go through that diagram and teach us how to read it?


I'd be happy to.

Purpose of the whole function is to set or clear the variable *B_ldsua*. That is the signal to the N249. So if B_ldsua = true, then N249 is activated, if B_ldsua = false, N249 is turned off.

Start far right @ that variable and work your way left.










*B_ldsua* is true IF *B_ldsuad* OR *B_ldsuas* are set to true. Both of those vars are set by a 'flip-flop' (*FF*). All that means is than once it's set to true, it stays true until it's reset manually. Like a light switch. You turn it on and it stays on until you turn it off. You can walk away and it stays on. You don't keep you hand on it. So you could be the one to turn the light on. While someone else could be responsible for turning it off.

So, once a condition is met, the flip-flop is set. just because the condition is no longer met, doesn't mean the flip-flop is cleared/reset. Some other, possibly unrelated condition, is responsible for resetting it.

S = condition to set the FF
R = condition to reset/clear the FF
Q = output of FF

That should get you going. Feel free to ask anything about it.


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## elRey (May 15, 2001)

Let's start with *B_ldsuas*. This is the cruise function mentioned by *Chickenman35*.










pvdkds_w = actual boost (MAP)
pu_w = ambient pressure (baro, changes with altitude)
nmot = RPM
SVDLDUVS = all 0

This function was intended to keep DV open under cruise like conditions to improve MPG. It compares pressure *ratio* (actual boost / ambient pressure) to output from SVDLDUVS map (RPM dependent). If pressure ratio is less than ( < ) SVDLDUVS then B_ldsuas = true.

Since the MAP is pre-TB, The MAP will never see below ambient pressure. So, the lowest pressure ratio can be is 1. In a stock 1.8T the map SVDLDUVS is filled with zeros.
So, this condition is never true.

note: there is no reference to pedal position.

I'd like to enable this function some time and see if it improves MPG noticeably.


Now, this is the reset/clear condition for *B_ldsuas*. If this condition is true, then B_ldsuas = false:











As you can see there are two ways B_ldsuas can be reset.

1) there is hysteresis about SVDLDUVS by amount HSSLDSUA
2) hysteresis about ambient pressure + LDUVRS and requested boost by amount HSLDSUA

So, if requested boost raises above ambient + LDUVRS +HSLDSUA, then flip-flop is reset and B_ldsuas = false.




__________________________________________________


Now for the other, primary way ME7 1.8T activates the N249, setting *B_ldsuad*.










B_ldsuad flip-flop is set by output of the *|&|* seen here on the left. That *|&|* has 3 inputs. *ALL* of which have to be true in order for the output to be true and B_ldsuad set to true. *Repeat, ALL 3 conditions here have to be met for B_ldsuad to be true.*

Let's look at each one separately.

The easiest one is the lower input:










wped = pedal position
nmot = RPM
SDKSUA = ALL 100%

If pedal position is less than OR equal to output of SDKSUA then this condition = true. The stock SDKSUA map is filled with 100%. So, this condition is always true. It can be ignored.


____________


The next, upper input deals with the pedal gradient:










dwped = pedal gradient, delta position (current position - previous position)
GWPLDU = -1.953%

If pedal delta is less than GWPLDU then this condition = true. And stays true for 0.1 sec even after delta stops being less than GWPLDU (hysteresis).


____________


The last, middle input deals with actual/requested pressure:










plsol_w = requested boost
pvdkds_w = actual boost
nmot = RPM
pu_w = ambient pressure

PIDLDSUA = 3
KFSDLDSUA = mostly 200hPa

If delta boost error * PIDLDSUA + current boost error is greater than ( > ) output of KFSDLDSUA then condition = true

(current[actual boost - requested boost] - previous[actual boost - request boost]) * 3 + current[actual boost - requested boost] > 200hPa

Even if you keep actual boost constant, a decreasing request boost (letting off gas) with cause this condition to be true.

When you see a 0 -> |MX| it's just taking the MAX value (0, input). Meaning it's keeping any values 0 or great (positive values).


_____________


The reset/clear condition for B_ldsuad:


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## Sim (Jun 27, 2002)

elRey said:


> Let's start with *B_ldsuas*.
> pressure ratio can be is 1. In a stock 1.8T the map SVDLDUVS is filled with zeros.
> So, this condition is never true.


If this was filled with valid data, would it cause to get the DV opened any time boost is higher that a pre set value?


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## elRey (May 15, 2001)

Sim said:


> If this was filled with valid data, would it cause to get the DV opened any time boost is *lower* that a pre set value?


^ Correction. It's a 'less than' comparison.


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## Sim (Jun 27, 2002)

elRey said:


> ^ Correction. It's a 'less than' comparison.


Wait, if it keeps dv open until a certain amount of pressure builds up, how could it reach any boost at all?


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## elRey (May 15, 2001)

Then come the Reset/clear condition which can be independent of the set condition. I was planning to cover the Flip-Flop reset conditions later.

Feel free to look at complete function for the reset condition. Hint: it looks at requested boost.


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## Sim (Jun 27, 2002)

Ah OK! BTW: This is way too complicated.

EDIT: Which has higer priority in the case both conditions are true? Set or reset?


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## groggory (Apr 21, 2003)

Sim said:


> Ah OK! BTW: This is way too complicated.


That's control logic for ya


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## elRey (May 15, 2001)

I added the reset condition to the B_ldsuas post.


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## groggory (Apr 21, 2003)

I'm going to try to explain what each item in this diagram means.

I'll be updating this image as I get a better handle on this. Thanks ElRey for taking the time to teach us how to read this stuff.


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## elRey (May 15, 2001)

I've expanded the post with more information: http://forums.vwvortex.com/showthre...p-the-N249&p=84617263&viewfull=1#post84617263

And it's just Rey :thumbup:


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## elRey (May 15, 2001)

Sim said:


> Which has higer priority in the case both conditions are true? Set or reset?


Reset. If reset is true, then flip-flop is false regardless of set condition.


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## Twopnt016v (Jul 5, 2009)

So where do most people learn to read this stuff? It's pretty tech and seems difficult without help from someone...at first at least.


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## elRey (May 15, 2001)

*groggory*, small correction top, right :

if a >= 1
*or*
b >= 1
then C = TRUE
else C = FALSE


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## groggory (Apr 21, 2003)

elRey said:


> *groggory*, small correction top, right :
> 
> if a >= 1
> *or*
> ...


Fixed. Also, added a bunch more explanations on there. Would you mind filling in the blanks please?


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## Dave926 (Mar 30, 2005)

The FR for ME7, Google Translate/Search, and lots of time. Reading assembly probably helps too.


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## Sim (Jun 27, 2002)

elRey said:


> And it's just Rey :thumbup:


LOL.  Yes, definitely :beer:.

I think these diagrams are a lot more easier to create than to understand .


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## Sim (Jun 27, 2002)

Meanwhile, I did some additional logs on my car ([email protected], DV=710N, no N249). I put a MAF in it, though it reads a bit higher as my tune is not calibrated to this extact part#, but this do not play any role in the actual log at all (the ECU still runs on a MAFless basis).

What I did was the same as i did before, just flooring the car and then suddenly letting off throttle (at possibly near maximum compressor rpms), but this time with logging the MAF output voltages, too.



Immediately (this can be considered "immediately" for real) the MAF voltage goes below 1V (zero g/s reading), which means that air is flowing backwards the MAF. The voltage waveform is a little bit hairy (no doubt), but i dont think that it would be a compressor surge at all. The "air flowing backwards" (ventig) condition lasts for around 0.65 seconds, at the end of this the intercooler pressure (MAP) is 115kPa.











The next one i did is a lot more interesting! I have disconnected the control hose/line (which is on the top of the DV) plugged the hose (of course) but left the "orifice" on the top of the DV opened to show how does a compressor surge look like in this case. I floored the car (requested boost is same as before), but the boost could not go past ~0.7bar this way. Probably the DV got opened, because there wasnt any boost on the top if it which would (help) to keep the DV closed and help to withstand the pressure entering from the side or from below (does not really matter IMO). So, this is probably the pressure difference between charge piping and real manifold pressure which is needed to open the 710N DV (actually the cut off point on the boost build up is at 0.5bar). This pressure difference is already available before(!) the spiking of the pressure in the intercooler piping and before the TB would reach 5%. The MAF voltage also shows the vigorous oscillation of air in the intake (compressor surge). This waveform is not similar to the one on the previous log.


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## groggory (Apr 21, 2003)

Sorry if it was already covered, but what is the green graph showing?


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## Sim (Jun 27, 2002)

groggory said:


> Sorry if it was already covered, but what is the green graph showing?


That is the real intake manifold pressure (not the one that ME7 sees).


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## Sim (Jun 27, 2002)

By the way, the car felt a lot more responsible with the DV kept closed during the usual cruising (10-15% tps)! Maybe n249 could have an alternate use, to keep the dv closed (ambient pressure directed to DV instead of the manifold boost / vacuum) when excessive pressure has been already exhausted/diverted but driver does not want full throttle (so when the DV needs the boost to stay closed).


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## elRey (May 15, 2001)

Sim, can you tap the N249 signal wire and log when ECU ties to open DV. I'm not asking you to install the N249, just log when ECU would open it. ECU grounds the solenoid.


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## Sim (Jun 27, 2002)

elRey said:


> Sim, can you tap the N249 signal wire and log when ECU ties to open DV. I'm not asking you to install the N249, just log when ECU would open it. ECU grounds the solenoid.


I will try to. It wont be easy as i am not runnng my original ECU (these logs arent done by the me7). I can put it back in no time (since my harness is still oem), thoug i wont be able to make logs, except for VCDS which is "nearly" useless. I was thinking about leading two wires into the car and putting a led on it (+a low ohms high wattage resistor to substitue the n249) so at least i will be able to see when it works.


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## BW-Boosted (Jan 3, 2014)

If you want, you can do the same test I did. I logged the pressure at compressor inlet to see REAL compressor surge. 
You can remeber my chart? Ambient pressure was ~990mbar. While shifting you can see peaks up to 1050mbar


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## groggory (Apr 21, 2003)

elRey said:


> Sim, can you tap the N249 signal wire and log when ECU ties to open DV. I'm not asking you to install the N249, just log when ECU would open it. ECU grounds the solenoid.


Mr. Rey,

Would you mind taking a look at my symbol diagram from that post and explain the symbols that I have red numbers next to please?

Sim,

Your logs are awesome. It has my head spinning as to all the variables. When the throttle body closes the N75 likely opens to blow off the turbo charge but the turbine still takes time to spin down. The 710n has a limited size orifice so it can only blow off the pressure at a given rate. The compressor wheel slows at a rate equal to the turbine slowing down but it still builds pressure during this slow down. If there is a pressure that spikes and then decreases on the charge pipe side of the 710n and the 710n's vacuum builds at a certain rate, at what differential pressure will the 710n begin to open, and when will it fully open. What is the correlation between how fast the compressor wheel has to spin and what pressure it can make...or more to the point, how does this relate back to how fast the turbine has to spin before the charge air can go backwards through the compressor wheel?

lol. This is starting to become quite the neat little experiment. I wish Sim had a RPM shaft speed sensor installed. That would be awesome.


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## Sim (Jun 27, 2002)

BW-Boosted said:


> If you want, you can do the same test I did. I logged the pressure at compressor inlet to see REAL compressor surge.
> You can remeber my chart? Ambient pressure was ~990mbar. While shifting you can see peaks up to 1050mbar


Yes, every log comes handy! Though you can hear your turbo surging (for some reason) so you will probably measure surging, too.
I cannot hear any surging nor fluttering (with the dv connected properly) and my MAF voltages are smooth, too.
Maybe you could record (log) your MAF voltage too (by tapping it).


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## Sim (Jun 27, 2002)

groggory said:


> Sim,
> 
> Your logs are awesome. It has my head spinning as to all the variables. When the throttle body closes the N75 likely opens to blow off the turbo charge but the turbine still takes time to spin down. The 710n has a limited size orifice so it can only blow off the pressure at a given rate. The compressor wheel slows at a rate equal to the turbine slowing down but it still builds pressure during this slow down. If there is a pressure that spikes and then decreases on the charge pipe side of the 710n and the 710n's vacuum builds at a certain rate, at what differential pressure will the 710n begin to open, and when will it fully open. What is the correlation between how fast the compressor wheel has to spin and what pressure it can make...or more to the point, how does this relate back to how fast the turbine has to spin before the charge air can go backwards through the compressor wheel?
> 
> lol. This is starting to become quite the neat little experiment. I wish Sim had a RPM shaft speed sensor installed. That would be awesome.


Thanks! Yes, i wish i had. Btw i am not sure that i could do any other logs (with new sensors/variables) which could prove that manifold "vacuum" is just enough to operate the DV.


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## BW-Boosted (Jan 3, 2014)

At the moment I cant log, because there are many issues. Flywheel and air intake.
Here's another chart, where i displayed the pressure between air filter and Turbo. (black line)

Blue and red is the same like in the other charts.
You can see, that the pressure is higher than ambient while shifting


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## Sim (Jun 27, 2002)

BW-Boosted said:


> At the moment I cant log, because there are many issues. Flywheel and air intake.
> Here's another chart, where i displayed the pressure between air filter and Turbo. (black line)
> 
> Blue and red is the same like in the other charts.
> You can see, that the pressure is higher than ambient while shifting


Yes i can see it (though i could not decipher the exact pressure  )
Cant it be due to DV is opening the high and low pressure parts of the turbo together?
DV vents air just exactly there (between turbo inlet and air filter).


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## Sim (Jun 27, 2002)

Sim said:


> Yes i can see it (though i could not decipher the exact pressure  )
> Cant it be due to DV is opening the high and low pressure parts of the turbo together?
> DV vents air just exactly there (between turbo inlet and air filter).


EDIT: Found the pressures .


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## suffocatemymind (Dec 10, 2007)

Sim said:


> By the way, the car felt a lot more responsible with the DV kept closed during the usual cruising (10-15% tps)! Maybe n249 could have an alternate use, to keep the dv closed (ambient pressure directed to DV instead of the manifold boost / vacuum) when excessive pressure has been already exhausted/diverted but driver does not want full throttle (so when the DV needs the boost to stay closed).


Excellent observation and hypothesis. That claim backs up my "N249 malfunction" code I get when using the N249 with my modified Evo DV...it can - unassisted by boost to the top nipple - hold ~35-40psi before cracking. Maybe there's a part-throttle condition where the ECU uses the N249 to assist in regulating boost to 0.5 bar...which simply can't happen with my car...

Great thread.


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## Sim (Jun 27, 2002)

Sim said:


> By the way, the car felt a lot more responsible


LOL, maybe thats not the right word, but you know what i mean .


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## Sim (Jun 27, 2002)

I have installed my stock ME7 ECU in the car. It is a 150HP one (actually they advertise it as 156HP) with the max boost of ~0.5bar (7-8 psi). The car has the stock intake and exhaust on it, except for the N249 (which has been deleted 10 years ago  ). I connected a 100Ohms 5W resistor (to fool the ECU) and a red LED (instead of the solenoid) so i could see when the N249 worked.

I could not get the N249 activated during a 100% full throttle run, even with the wastegate line disconnected from the N75 (causing serious overboost conditions). I have to admit that *i was wrong* regarding to this. N249 activates only at negative throttle pedal transients, elRey you were right!

BUT (and i think here comes the culprit) i could get the N249 to stay activated after such a negative throttle transient for way too long.

For example when i want the car to get moving (a bit faster than usual), i usually press the throttle lets say to ~30% and keep it there until the car actually starts off and then i am pressing it more further to lets say to ~60%. When i could not keep my foot exactly at the same (constant) position (due to acceleration or even a bump!) i could accidentally trigger the N249 (with a small negative throttle movement) and then pressing the pedal more further to ~60% did not immediately deactivate the N249 (only after a sec). 

The same may happen if you are just letting off throttle (not completely) and then pressing it again (generously but not 100%).

I shot a short video showing some of these accelerations (even up to full boost!), with the N249 being activated by the ecu.






EDIT: typo


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## elRey (May 15, 2001)

Very good find about the delay in deactivating N249 !
Maybe we can look at function and guess whats happening.

I like the LED. I have one also right in front of my boost gauge. But mine is connected to out of N75 so I can monitor Wastegate duty. :thumbup:


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## Sim (Jun 27, 2002)

elRey said:


> Very good find about the delay in deactivating N249 !
> Maybe we can look at function and guess whats happening.
> 
> I like the LED. I have one also right in front of my boost gauge. But mine is connected to out of N75 so I can monitor Wastegate duty. :thumbup:


If it had the n249 i would have to press the pedal more agressively to gain any boost at all (as turbo would be bypassed). The more agressive throttle would probably deactive it. However, this way (n249 deleted) i have a "decent" amount of boost as you can see.I am usually applying the throttle pogressively as the rpm rises (i have found the car to accelerate better this way) and this does not seem to be enough for this function to get out of the bypassed condition (in some cases). (BTW: This is still not the answer to my rattling DV experiences.)

As far as i know turbos are there to increase the efficiency of an engine. IMHO there is no reason to keep the turbo bypassed during acceleration (any kind of acceleration (even if it is not full throttle)).


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## Rawcpoppa (Oct 17, 2011)

Alot of technical info in here. Is the debate officially over? I have a more recent document that might help shed some light but it's for a different engine...


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## rstolz (Jun 16, 2009)

While it was posed as an argument to keep the N249, it really morphed into a discussion of the merits/demerits of keeping it vs bypassing it.

Keeping it allows a tighter control over your boost and pressures, smoothing out spikes and improving partial throttle response.

Bypassing it greatly simplifies the system, but you live with a bit more risk, as boost as a bit more freedom.

The system may be able to be manipulated or upgraded for an extreme amount of boost control, but the effort involved would be huge, for what would largely be a negligible gain as far as the majority of users would be concerned.

it's like using a choke collar, or an invisible fence on your dog.

The invisible fence is like bypassing the N249: It'll be kept under control most of the time, but there's still that small chance it could get past the fence and cause trouble.

The choke collar is the N249: as soon as it looks like boost is going to get wild, the N249 gives a tug on the choker, and gets it back in line.


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## Rawcpoppa (Oct 17, 2011)

Would you say how the N249 is applied is unique to each engine code or it basically does the same thing for each engine? I've been researching and came across a document for a 1.4 litre supercharged + turbocharged engine from VW that has the N249 valve as well.


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## groggory (Apr 21, 2003)

Let's lay down some summaries of this thread to help with some solid FAQ material. I would work on them but I'm impacted on time right now. You guys start and we'll pick it up.

I think this will be an excellent addition to the FAQ


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## elRey (May 15, 2001)

It comes down to personal preferences. All the Objective reason for either side are insignificant:
weight, turbo life, etc

I does not interfere with boost because it does not play a role in overboost protect.

My subjective observation is that is smooths out coming off throttle transition and allows a bit faster respool during gear changes. I say subjective, b/c the measured affect is insignificant (small).

Only valid reasons against it is clean wiring, less items to fail, less hoses to leak. 

Personal Preference.


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## groggory (Apr 21, 2003)

elRey said:


> It comes down to personal preferences. All the Objective reason for either side are insignificant:
> weight, turbo life, etc
> 
> I does not interfere with boost because it does not play a role in overboost protect.
> ...


So...

Removing N249 smooths out coming off throttle transitions to a minor degree

Removing N249 allows a bit faster respool (to a minor degree) during gear changes (due to the ECU holding the N249 open excessively long)

Removing the N249 removes the vacuum canister and a fair amount of vacuum hoses (in addition to removing the N249).

If you remove the N249 you must resistor in order to keep fuel trims

Keeping the N249 allows your ECU to protect your engine in certain conditions. The N249 does not protect against overboost.


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## elRey (May 15, 2001)

groggory said:


> So...
> 
> Removing N249 smooths out coming off throttle transitions to a minor degree
> *opposite*
> ...


opposite, n249 smooths and reduces respool.


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## Rawcpoppa (Oct 17, 2011)

Summarizing helps alot I think because as much as the previous pages are informative alot of it is very confusing.










Does your summary line up with what is in this document or is the summary pretty much only for 1.8T?

edit- image is from this document for reference: http://www.volkspage.net/technik/ssp/ssp/SSP_359.pdf


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## elRey (May 15, 2001)

read my comments to your post above


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## groggory (Apr 21, 2003)

elRey said:


> I does not interfere with boost because it does not play a role in overboost protect.


You said that ^^




groggory said:


> Keeping the N249 allows your ECU to protect your engine in certain conditions. The N249 does not protect against overboost.


So I summarized it by saying that ^^




elrey said:


> this contradicts itself.
> the latter is true


But then you said that ^^ in regard to my previous statement.

I'm confused. I think either my comprehension is poor or we are communicating poorly.

Would you please summarize this thread being that you have the best understanding of what's happing using clear, concise, individual statements like I was writing?


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## elRey (May 15, 2001)

elRey said:


> I does not interfere with boost because it does *not* play a role in overboost protect.





groggory said:


> Keeping the N249 allows your ECU to protect your engine in certain conditions. The N249 does not protect against overboost.




Let's break that statement down..




groggory said:


> Keeping the N249 allows your ECU to protect your engine in certain conditions.


N249 and ECU are effectively the same thing since the ECU uses the N249, and the N249 can not act on it's own.

So, here you are saying the N249 protects the engine, and since it can only release boost, that mean it can only protect from overboost.




groggory said:


> The N249 does not protect against overboost.


Here you are saying it does not protect from overboost, which is the same as I said.


I think the confusion comes from the fact that I didn't clearly state that I'm *IN FAVOR *of *KEEPING* the N249.


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## groggory (Apr 21, 2003)

elRey said:


> Let's break that statement down..
> 
> 
> 
> ...


I should have broken my statement up into atomic parts so you could agree or disagree on specific parts.

I would imagine the N249 would be used by the ECU in other situations to protect the engine. Perhaps when the ECU slams the throttle body shut due to a different engine issue the N249 would also be triggered to blow off whatever boost is going on. I'm not really sure. I'm just guessing. All I wanted to do was lay out each pro and con of keeping and removing the N249. Obviously people can make their own decisions, I was just trying to build up some cliff's notes.


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## elRey (May 15, 2001)

groggory said:


> I should have broken my statement up into atomic parts so you could agree or disagree on specific parts.
> 
> I would imagine the N249 would be used by the ECU in other situations to protect the engine. Perhaps when the ECU slams the throttle body shut due to a different engine issue the N249 would also be triggered to blow off whatever boost is going on. I'm not really sure. I'm just guessing. All I wanted to do was lay out each pro and con of keeping and removing the N249. Obviously people can make their own decisions, I was just trying to build up some cliff's notes.


Operation of the N249 is completely limited to one condition, and that is when pedal position decreases. Nothing else triggers N249. Nothing. There are limited DBW 1.8T models that do utilize the N249 during cruise to keep DV open for fuel consumption, but I've yet to see one in the states. Outside of that, the N249 not used. Even if overboost skyrockets.


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## groggory (Apr 21, 2003)

Summary

Keeping the N249 smooths out coming off throttle transitions to a minor degree.

Keeping the N249 allows a bit faster respool (to a minor degree) during gear changes

Removing the N249 removes the vacuum canister and a fair amount of vacuum hoses (in addition to removing the N249).

If you remove the N249 you must resistor in order to keep fuel trims

The N249 can open only under a negative pedal position slope. No other condition will cause the N249 to open. 

A negative pedal position slope does not necessarily mean the N249 will open under all circumstances.

The N249 will not protect against overboost.

----------------------------------------------------------------

All N249 Logic can be seen here in the official Bosch Logic Diagrams.

The operation of the N249 can be seen here. When the LED turns on that is the N249 activating. The boost gauge is manifold pressure.

You can see the entire system working here. This shows RPM, Throttle Body Position, Charge Pipe Pressure, Intake Manifold Pressure, MAF flow (g/s), MAF voltage (1v is zero flow)


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## Rawcpoppa (Oct 17, 2011)

If n249 allows for faster respool during gear change but only opens under negative pedal position slopes how does it do anything during gear changes?


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## elRey (May 15, 2001)

Rawcpoppa said:


> If n249 allows for faster respool during gear change but only opens under negative pedal position slopes how does it do anything during gear changes?


Do you not let off the pedal when you change gears? barring NLS


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## elRey (May 15, 2001)

groggory said:


> Summary
> 
> Keeping the N249 smooths out coming off throttle transitions to a minor degree.
> 
> ...




:thumbup::thumbup::thumbup:


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## Rawcpoppa (Oct 17, 2011)

elRey said:


> Do you not let off the pedal when you change gears? barring NLS


I have a 7 speed dsg so keep my foot planted on the accelerator. Not sure what the car does under gear changes electronically.


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## groggory (Apr 21, 2003)

Thread and summary added to FAQ under electrical and cross referenced to n249


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## elRey (May 15, 2001)

Rawcpoppa said:


> I have a 7 speed dsg so keep my foot planted on the accelerator. Not sure what the car does under gear changes electronically.


Hmm. I don't think our 1.8T 20v (current forum) discussion applies to your car.


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## Rawcpoppa (Oct 17, 2011)

Ok cool. Was curious as the two different engines both carry N249 valves but I guess the execution might be a little different.


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## rstolz (Jun 16, 2009)

> Rawcpoppa
> Why you should keep the N249.......
> 
> Ok cool. Was curious as the two different engines both carry N249 valves but I guess the execution might be a little different.


It's not the execution that's different, it's where it gets the signal to open from. the signal is going to come from the throttle cut that occurs between DSG shifts.


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## Dave926 (Mar 30, 2005)

Bringing this back from the dead?

Compromise for deleting the n249?

http://www.turbosmartdirect.com/Product-Categories/BOV-Controller/BOV-controller-kit-controller-and-hardware-only-NO-BOV-BLACK.html


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## elRey (May 15, 2001)

Nifty. I would think relieving pressure before TB closes would allow smaller turbos to continue spinning more so than larger turbos that have more inertia.


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## gitman (May 13, 2004)

elRey said:


> Very good find about the delay in deactivating N249 !
> Maybe we can look at function and guess whats happening.


Just got through this whole thread, I was hoping there would have been more follow-up in regards to the deactivation delay. regardless, thanks for all the great info!


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## elRey (May 15, 2001)

Sim said:


> ...
> BUT (and i think here comes the culprit) i could get the N249 to stay activated after such a negative throttle transient for way too long.
> 
> For example when i want the car to get moving (a bit faster than usual), i usually press the throttle lets say to ~30% and keep it there until the car actually starts off and then i am pressing it more further to lets say to ~60%. When i could not keep my foot exactly at the same (constant) position (due to acceleration or even a bump!) i could accidentally trigger the N249 (with a small negative throttle movement) and then pressing the pedal more further to ~60% did not immediately deactivate the N249 (only after a sec).
> ...





elRey said:


> Very good find about the delay in deactivating N249 !
> Maybe we can look at function and guess whats happening.
> 
> I like the LED. I have one also right in front of my boost gauge. But mine is connected to out of N75 so I can monitor Wastegate duty. :thumbup:





gitman said:


> Just got through this whole thread, I was hoping there would have been more follow-up in regards to the deactivation delay. regardless, thanks for all the great info!



So, Sim was describing a behavior where the N249 remained active after a negative pedal gradient had stopped and a positive pedal gradient had started.

We have to refer to the Reset part of the function to see if we can explain this behavior:



elRey said:


> ...
> 
> The reset/clear condition for B_ldsuad:


B_ll = idle condition
dwped = pedal gradient, delta position (current position - previous position)
GWPLDUR = 1.953%

There are three ways to deactivate the N249 (3 paths to the >= 1 box):

(top to bottom)
1) Transition from idle.
2) If pedal delta is greater than GWPLDUR. And stays true for 0.1 sec even after delta stops being greater than GWPLDUR (hysteresis).
3) Automatically resets itself THLDUVD seconds after being activated.

And Reset trumps Set if both conditions are true.

Seems only way to explain behavior is if Sim was moving pedal so slowly as to keep positive pedal gradient below GWPLDUR which I believe is 1.953%. Seems hard to believe he could do that. So, I don't know why he experienced that behavior. Can anyone reproduce his finding?


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## Dave926 (Mar 30, 2005)

I can add to the fact that between shifts with my 3071r it only drops to 4-5psig on a 15psig wastegate spring. If I change the spring in my 008 to one appropriate for my current boost I bet it will drop less. Still using the n249.

There is a log in my build thread Ill post here later.if necessary.


----------

