# TT losing all boost at 4-5k RPM



## Holtzy822 (Oct 20, 2014)

Hey guys, having a bit of a problem with my TT recently. Car is pretty much stock except an intake but Ill be pushing about 10lbs (as per the boost gauge) all the way to about 4.5-5k rpm, instead of the boost tapering off, I just lose all boost, I'm thinking that it could be the wastegate opening but I don't hear it vent like I normally do through the intake. It didnt bother me until today when I went to pass someone on an on ramp and had to back off after I lost boost. Any ideas?


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## Gonzalo1495 (Feb 2, 2015)

Quick question. Does your car HOLD boost except after you hit that range, or is it a progressive loss. From what you've described it can't possibly be a boost leak that wouldn't be noticeable. It could be your waste-gate actuator honestly. I don't think I've ever experienced this problem before so not too sure my experience will help out here.


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## Holtzy822 (Oct 20, 2014)

Gonzalo1495 said:


> Quick question. Does your car HOLD boost except after you hit that range, or is it a progressive loss. From what you've described it can't possibly be a boost leak that wouldn't be noticeable. It could be your waste-gate actuator honestly. I don't think I've ever experienced this problem before so not too sure my experience will help out here.


Yes, it'll hold 10lbs until between 4-5k then it'll just dump all of it, I have all new boost hoses in the car so I kinda ruled that out.


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## nbkkb7x (Jan 12, 2009)

I would do a pressure test on your boost system. Take off your intake and MAF and hook a unit up to your TIP. I use a PVC cap with a vacuum hose connected and slowing increase pressure. If all this checks out you know it's happening on the wastegate side of things.

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## TTopless (Oct 5, 2015)

any cel ? mine was doing that and had a code for o2 sensor.... cleared it and ran fine.


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## Holtzy822 (Oct 20, 2014)

TTopless said:


> any cel ? mine was doing that and had a code for o2 sensor.... cleared it and ran fine.


Yeah, but I've had it for a while for unplugged MAF sensor, I have a new sensor, just haven't put it in... Waiting for a new intake


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## Volksdude27 (Nov 25, 2005)

Sounds like inlet collapsing. I had the exact same issue when my silicone inlet was too close from abs lines. 4500-5000k lost all boost. Try search audi TT inlet collapsing on google you'll find many useful info. If it is best bet is silicone inlet.

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## Holtzy822 (Oct 20, 2014)

Like the Turbo inlet pipe? Ill go take a look at it...


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## Holtzy822 (Oct 20, 2014)

no luck, hose is fine, no tears and is in good condition.


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## Holtzy822 (Oct 20, 2014)

Happy days! Unplugged the n75 from the waste gate and bam! Boost all the way past 5k (didn't go WOT) anyways, my friend had a forge 3 prong MBC laying around so I decided to put it in until I can get a new n75, only problem is it's only making 8psi whether it's all the way screwed in or backed all the way out. The way I have it set is the bottom nipple plugged into the TIP (atmospheric vent I believe), waste gate hose in the right nipple and turbo boost hose in the left, same way it was set up on the n75, did I install it backwards or will the MBC just not go over 8psi... I like the onset of the boost, just wish there was more of it. 

Also weird fact, in the year I've owned my TT it's never started the first try when cold, for some reason or another it started first try when I disconnected the WG hose on the n75 and I hadn't driven it in over a day.


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## Marcus_Aurelius (Mar 1, 2012)

Holtzy822 said:


> Happy days! Unplugged the n75 from the waste gate and bam! Boost all the way past 5k (didn't go WOT) anyways, my friend had a forge 3 prong MBC laying around so I decided to put it in until I can get a new n75, only problem is it's only making 8psi whether it's all the way screwed in or backed all the way out. The way I have it set is the bottom nipple plugged into the TIP (atmospheric vent I believe), waste gate hose in the right nipple and turbo boost hose in the left, same way it was set up on the n75, did I install it backwards or will the MBC just not go over 8psi... I like the onset of the boost, just wish there was more of it.
> 
> Also weird fact, in the year I've owned my TT it's never started the first try when cold, for some reason or another it started first try when I disconnected the WG hose on the n75 and I hadn't driven it in over a day.


I believe that's an improper way to plumb a MBC as a standalone. Pressure source goes to the inlet port of the MBC -- oulet port is directed to the wastegate actuator niple. Also make sure you unhook the N75 and loop/plug the ports shut, the electrical need to remain in the loop however.


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## Holtzy822 (Oct 20, 2014)

Problem is, which is the inlet, which is outlet, and which is the bleed. I thought the two on the sides were inlet/outlet so it should be correct. That's where I have the pressure line and line going to the WG


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## Marcus_Aurelius (Mar 1, 2012)

What MBC are you using, do you have some pics? Unless you give us more, it's hard to tell you what you're dealing with. 

Most common and conventional mechanical MBC are two port devices with a ball and spring in a cylinder. The ball blocks the inlet port in the cylinder and the spring keeps adjustable tension on it until the intern preload is exceeded by system pressure. Once that's done pressure is allowed to flow through to activate the wastegate actuator. If you have a 3-port MBC (very rare) boost is also allowed to help keeping tension on the ball but it's still the same concept and plumbing. Now, there a are also bleed type MBC and those are constant bleed devices and not recommended, think of those as permanent leaks and a subpar design. There are also the pneumatic type valves that can have multiple ports, and those are harder to setup and figure out since they can be constructed is various port layouts.


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## Holtzy822 (Oct 20, 2014)

Marcus_Aurelius said:


> What MBC are you using, do you have some pics? Unless you give us more, it's hard to tell you what you're dealing with.
> 
> Most common and conventional mechanical MBC are two port devices with a ball and spring in a cylinder. The ball blocks the inlet port in the cylinder and the spring keeps adjustable tension on it until the intern preload is exceeded by system pressure. Once that's done pressure is allowed to flow through to activate the wastegate actuator. If you have a 3-port MBC (very rare) boost is also allowed to help keeping tension on the ball but it's still the same concept and plumbing. Now, there a are also bleed type MBC and those are constant bleed devices and not recommended, think of those as permanent leaks and a subpar design. There are also the pneumatic type valves that can have multiple ports, and those are harder to setup and figure out since they can be constructed is various port layouts.


It was a forge 3 prong bleed type, my friend just had it laying around so I figured it would do until a new n75 came in, it's the same one ECS still sells, I'll go out and take a picture when my car is cooled down


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## Marcus_Aurelius (Mar 1, 2012)

Holtzy822 said:


> It was a forge 3 prong bleed type, my friend just had it laying around so I figured it would do until a new n75 came in, it's the same one ECS still sells, I'll go out and take a picture when my car is cooled down


Ok, bottom is the bleed port (going to the intake), and the two opposite side ports are interchangeable for manifold or wastegate actuator routing.


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## Holtzy822 (Oct 20, 2014)

Marcus_Aurelius said:


> Ok, bottom is the bleed port (going to the intake), and the two opposite side ports are interchangeable for manifold or wastegate actuator routing.


That's how I have it set, still no boost control, only 8 psi, any thoughts?


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## Marcus_Aurelius (Mar 1, 2012)

Holtzy822 said:


> That's how I have it set, still no boost control, only 8 psi, any thoughts?


Too strong of a spring installed, a faulty unit etc. could all be causes. Do you still have the N75 hooked up?


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## Holtzy822 (Oct 20, 2014)

Marcus_Aurelius said:


> Too strong of a spring installed, a faulty unit etc. could all be causes. Do you still have the N75 hooked up?


yup n75 is still plugged in. As of right now (test drove 30 secs ago) It will build quickly to 10, hold at 8 until about 4k and taper off until redline...


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## Holtzy822 (Oct 20, 2014)

Marcus_Aurelius said:


> Too strong of a spring installed, a faulty unit etc. could all be causes. Do you still have the N75 hooked up?


Thinking about buying a new mbc instead of n75, thoughts?


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## Gonzalo1495 (Feb 2, 2015)

Holtzy822 said:


> Thinking about buying a new mbc instead of n75, thoughts?


Forge Unos :thumbup:
Glad you found out the problem though!


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## Marcus_Aurelius (Mar 1, 2012)

Yes, I think that's the best thing to do. Get a Forge Uno-s MBC, it's a two port non-bleed type unit and about the best MBC you can buy. Make sure you keep the N75 electrically hooked up, but plug all the port shuts.


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## Holtzy822 (Oct 20, 2014)

Gonzalo1495 said:


> Forge Unos :thumbup:
> Glad you found out the problem though!


nope. Started acting up again driving home, first gear had boost all the way through, second gear 5k exactly went to 0psi, could it be the spring on the wastegate is worn out?


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## Marcus_Aurelius (Mar 1, 2012)

Holtzy822 said:


> nope. Started acting up again driving home, first gear had boost all the way through, second gear 5k exactly went to 0psi, could it be the spring on the wastegate is worn out?


Could be, but I would seriously check if you don't have a collapsing TIP. I know it was mentioned before, but you can't visually check it, the car needs to be under load for the hose to collapse. What TIP is fitted? If it's stock, chances are it might be collapsing under load.


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## Holtzy822 (Oct 20, 2014)

Marcus_Aurelius said:


> Could be, but I would seriously check if you don't have a collapsing TIP. I know it was mentioned before, but you can't visually check it, the car needs to be under load for the hose to collapse. What TIP is fitted? If it's stock, chances are it might be collapsing under load.


How would I check it? I have a 180, thought the 180s didn't collapse like the 225s, doing the waste gate spring mod to see if the waste gate is just old (car has 162k on it)


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## Holtzy822 (Oct 20, 2014)

So I did the spring mod, and it held up to 10psi! Then tapered off, my theory is the gate is bad and was only holding 8psi (thus why I couldn't get it over that with the MBC) then when I put the spring on it helped keep it closed to 10psi, I'm going to put on a second spring and see how that goes


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## Gonzalo1495 (Feb 2, 2015)

Holtzy822 said:


> So I did the spring mod, and it held up to 10psi! Then tapered off, my theory is the gate is bad and was only holding 8psi (thus why I couldn't get it over that with the MBC) then when I put the spring on it helped keep it closed to 10psi, I'm going to put on a second spring and see how that goes


Well the spring is always going to add more as far as my knowledge goes, so I don't think you can make that call just yet? Unless I'm wrong and they don't affect boost. Idk I haven't done it yet.


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## Holtzy822 (Oct 20, 2014)

Note to self, doe pipe is still hot after 2 hours, going to be a nice scar... Didn't get the second spring on, ill do that tomorrow, other than that I'm totally out of ideas. I really don't want to replace both the n75 and the waste gate... That would be pricey


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## Holtzy822 (Oct 20, 2014)

threw the second spring on there, held ~11.5 psi and started to taper off at around 4500. No drop off at 5, just a smooth taper off. Ran fine for the first few pulls. On the highway it dumped again at 5. I find its always only at WOT in 2-5th, not 1st for some reason. Not ruling out collapsing TIP, just don't know how to test it.


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## Holtzy822 (Oct 20, 2014)

Unplugged the boost controller and put the n75 back on. Now I'm only building ~6 psi. Really starting to lose faith in this car lol


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## Marcus_Aurelius (Mar 1, 2012)

Holtzy822 said:


> I find its always only at WOT in 2-5th, not 1st for some reason. Not ruling out collapsing TIP, just don't know how to test it.


That means it's load dependent, as 1st gear isn't seeing loads seen in upper gears due to gearing. I would really go after testing and replacing the TIP, the more you describe the issue, the more it points to a collapsing TIP under load.


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## Holtzy822 (Oct 20, 2014)

Marcus_Aurelius said:


> That means it's load dependent, as 1st gear isn't seeing loads seen in upper gears due to gearing. I would really go after testing and replacing the TIP, the more you describe the issue, the more it points to a collapsing TIP under load.


I think it is too now. Going to replace the tip but that still doesn't explain the 6 psi boost.


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## Holtzy822 (Oct 20, 2014)

So I got my code cleared which was MAF unplugged but it's still only making 7 psi, almost like soft limp mode but it only started when I switched back from the MBC to n75... Any thoughts.


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## Sniper911 (May 30, 2015)

I had a similar issue with my TT a few weeks ago. I was loosing boost and couldn't get more that 8 or 9 lbs at any rpm though. I was all set to just upgrade the TIP thinking it was collapsing under load but then I started getting codes for misfires and lean mixes which generally indicate a vacuum leak. I couldn't find one for the life of me though until I smoked out the engine. Then I found it immediately and it just happened to be that the small vacuum hose under the intake manifold had come loose. Once I reattached it everything was right. No codes and all the boost I'm supposed to have. Having said that, have you definitely ruled out a vacuum leak? My first reaction to this thread was that it was either a vacuum leak or a collapsing or cracked/leaking TIP. There'a a lot of knowledgeable people on this forum and more than a few seems to be pointing to the TIP as their suspect.


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## 91MK2Jetta (Jul 25, 2012)

so youre saying you have a check engine light on? first problem is solve the light issue. Then move on to the boost issue. no point in trying to fix one thing if the other is still bad. you could be in soft limp mode. If you can't hold boost with a mbc then you have a boost leak somewhere


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## Holtzy822 (Oct 20, 2014)

Cel was for MAF unplugged, which is fine because I unplugged it. With the MBC I could get 11 psi fine. I have a small leak under my intake manifold that I'm going to fix today but I really don't think that could cause me to lose half my boost. I have another MAF waiting to go in, I'm just waiting on my new TIP to put it in. I had 2 seperate issues, first it would hit 5k under full boost and stop boosting (TIP collapsing) then it started to only let me boost to 6psi. I'm going to fix the leak and see how that goes


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## TheDeckMan (Sep 26, 2004)

A small leak will screw up everything boost/fuel related. Fix your leaks and make sure no leaks at 20psi.


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## Holtzy822 (Oct 20, 2014)

Leak is fixed but no luck. Still holding no more than 7 PSI. I have 2 springs on the wastegate but I don't see how that could possibly affect anything.... or maybe its not opening when the N75 wants it too... therefore thinking there's something wrong and limiting the boost.... going to wait for the turbo to cool off and going to take the springs off.


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## TheDeckMan (Sep 26, 2004)

Holtzy822 said:


> Leak is fixed but no luck. Still holding no more than 7 PSI. I have 2 springs on the wastegate but I don't see how that could possibly affect anything.... or maybe its not opening when the N75 wants it too... therefore thinking there's something wrong and limiting the boost.... going to wait for the turbo to cool off and going to take the springs off.


Is it chipped? 8psi is stock on a 180 and 15psi on a tune.


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## Holtzy822 (Oct 20, 2014)

TheDeckMan said:


> Is it chipped? 8psi is stock on a 180 and 15psi on a tune.


its stock but I've always gotten 11psi from it. I took off the wastegate springs and its now down to 5PSI. I dont think its limp mode because I got the code cleared last night and it was just my MAF unplugged which has never thrown me into limp mode before


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## Holtzy822 (Oct 20, 2014)

I fixed it. not saying what was wrong because it was incredibly stupid but its back to 11 psi. Now the TIP is just collapsing again, (happily) back to square 1.


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## Boulderhead (Oct 21, 2012)

Holtzy822 said:


> I fixed it. not saying what was wrong because it was incredibly stupid but its back to 11 psi. Now the TIP is just collapsing again, (happily) back to square 1.


You had N75 plumbed backwards? 


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## Holtzy822 (Oct 20, 2014)

Boulderhead said:


> You had N75 plumbed backwards?
> 
> 
> Sent from my iPad using Tapatalk


...yeah XD it was sideways


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## Holtzy822 (Oct 20, 2014)

Replaced the TIP and MAF today, TT is running like a charm, sounds amazing up at redline with the new 3" turbo back straight pipe


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## Marcus_Aurelius (Mar 1, 2012)

:thumbup::thumbup:


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