# N75 failure symptoms



## black_wolf (Feb 18, 2005)

Hey all, 
I have been battling a weird issue with my car for the last week or so. About a month ago I put on a APR 2.5 downpipe. Everything was fine, turbo spooled nicely, etc. 
Recently I have been having a strange issue with boost. Such that there is no such thing as 1psi -4psi of boost. It is either neutral (0psi, 0inHG) or 5psi and more. I have bypassed the N249 thinking that might have something to do with it, but to no avail. It did however clean up some surging issues I was having.
If i slowly roll into the throttle, then the there will be a point where it seems like a "switch" has been turned on and there is instant 5psi or more. I can back out of the throttle just slightly then it is like the "switch" is turned off and I am back at 0psi.
<EDIT> Also, (very randomly) sometimes If I slowly roll into the throttle, it will get stuck at 3psi or 4psi, no more, no less. If I lift off the throttle and go back into vaccume, then get back into boost, everything will be fine.<EDIT OFF>
I cleaned the throttle body thinking it might not be fully opening and readjusted it with the VAG-COM. I am getting 1 code for the N249 valve but I figure that is just because I have bypassed it. 
Any thoughts?
BTW-My mods are AEM intake, Blitz BOV/DV, APR 2.5 DP. Nothing major. All these started well after the DP install, so I am thinking it is not related.
Thanks



_Modified by black_wolf at 9:07 AM 5-20-2005_


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## black_wolf (Feb 18, 2005)

Anyone? Surely someone has had one fail.


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## Swampyankee (Jan 23, 2003)

*Re: N75 failure symptoms (black_wolf)*

Might be a bad O2 sensor. Running rich can foul it. Check it out. Sounds a little like what recently happened to mine.


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## DJKeebler (Dec 6, 2001)

I don't think the O2 sensor would cause the engine to bog like that. It wouldn't affect the A/F ratio in that manner. I could be wrong as I currently have a bad O2 sensor in my car that needs to be changed.
I would start with simple things like checking the spark plugs and running a bottle of good fuel injector cleaner through the tank. Also, you have a 2001 so check/change your fuel filter and make sure you don't have any boost leaks.


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## Chris164935 (Jan 10, 2004)

*Re: (DJKeebler)*

Sounds like the symptoms of a bad n75 valve. I've never had mine go bad, but it has come unplugged. Didn't trigger a chekc engine light, but the motor ran in hard limp mode (like what you were describing).


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## black_wolf (Feb 18, 2005)

*Re: (Chris164935)*

I have had mine unplugged accidentally and it was doing the same thing, but this time it is plugged in. I went and got a J valve and things are better, but they are still not perfect. I am however getting a CEL for lean between shifts. I tested my Blitz BOV (converted to a DV) and it isn't holding much vaccume. So, time to replace that. I think I will go back to stock to see if that is the problem.
Thanks for the help. I will post again when I get the stock DV on the car.


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## Mosquito (Mar 8, 2003)

I've had that happen to me. I've always belived it to be a mechanical issue driving it to run like that. I used different N75 valves and it happens with all of them, just less with some. I've always gotten the feeling that it has to do with the actuator and not the N75 valve itself. It seems to be the cause of surging too.



_Modified by Mosquito at 12:10 PM 5-21-2005_


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## 03VDUB (Sep 13, 2003)

*Re: (Mosquito)*

happened to a friend of mine.. Car dyno'd at 155 with full apr chip catback, TIP, CAI, DV.. replaced the n75 and was up to 190 i think.. He was always in limp mode..


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## black_wolf (Feb 18, 2005)

Ok, so here is a quick update. I replaced the Blitz BOV that I converted to a DV in favor of a brand new stock DV. After getting my hopes up, things took a turn back to being broken. 
So, I start to think, I have essentially changed the setup to a normal turbo setup, DV controlled by manifold pressure (not the N249) and the wastegate is controlled by the N75, but that has a new J valve on it so that has to be essentially working correct.
I decide to get out the ole trusty MityVac and just make sure the wastegate is working properly. The hose off the N75 to the wastegate is holding pressure so that looks okay. I decide to check the hose going into N75. 
Bingo, that wasn't holding pressure. So, I replace that line and things so far have been good. So, Knock of wood, I hope that was the problem. I have an autocross tomorrow so I should know if there will be any more issues tomorrow. Thanks to all those that chimed in with help.


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## black_wolf (Feb 18, 2005)

Well the autocross went well. No boost issues at all. However, on the way home, the problems started again, but not as bad. 
I am getting a the following on the VAG-COM:
17705 - Pressure Drop between Turbo and Throttle Valve (check D.V.!) P1297 - 35-00 - -
So, the DV is brand new. Looks like I have a boost leak somewhere. Now the fun begins of tracking that down.


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## [email protected] (Feb 28, 2001)

*Re: (black_wolf)*

yes you are correct thats a boost leak check the vac hoses 
also to answer you first question there is no way of N75 going bad unless its broken in pieces


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## 03VDUB (Sep 13, 2003)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_yes you are correct thats a boost leak check the vac hoses 
also to answer you first question there is no way of N75 going bad unless its broken in pieces 

Umm, no.. Your wrong.. Sorry to be blunt, but yes it is possible.. It has happened to a friend of mine, Looked to be perfect on the outside..


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## [email protected] (Feb 28, 2001)

*Re: (03VDUB)*


_Quote, originally posted by *03VDUB* »_
Umm, no.. Your wrong.. Sorry to be blunt, but yes it is possible.. It has happened to a friend of mine, Looked to be perfect on the outside.. 

what i ment is with or without the N75 there still will be pressure or vacume at the WG unless it gets clogged which probably is what happend to your friend


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## 03VDUB (Sep 13, 2003)

*Re: ([email protected])*

My friends problem had nothing to do with vacuum lines being clogged.. His N75 Malfunctioned, Why do you think that the n75 cannot break unless it is in pieces..


_Quote, originally posted by *[email protected]* »_
what i meant is with or without the N75 there still will be pressure or vacuum at the WG unless it gets clogged which probably is what happened to your friend


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## Mosquito (Mar 8, 2003)

I've had 2 N75 valves make ticking noises under light throttle and boost. The MBC bleeds boost at that exact point. I think a bad actuator might make a N75 malfuction. After all. It is still mechanical inside.


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## black_wolf (Feb 18, 2005)

Alright, we I hope to have a final posting about this. It seems that my problems lead back the the 2.0L MAF sensor I was running. Atleast when I put the original 1.8T MAF sensor in things have been running back to the way they should. 
I did some searching on the 17705 code that I kept getting. Three things seemed to be the common factor for that code. 
1: DV 
2: Intercooler piping hose leaks
3: 2.0L MAF sensor 
I remembered that I had put one on my car when this thing first started as a way to verify a CEL I had. uggg, this has been a Pain in the a**


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