I am having a big mystery from my car. Currently It seems to drive fine except it doesnt boost more than 0.2 bar. Car seems fine in whole revband just no boost.

Things that were checked:
Pressure tested.
Compressor wheel and exhaust wheels spins freely.
No smoking, no weird noises etc..
Wastegates are closed, tried running without N75 attached, without boost line to wastegate.
No exhaust leaks that I can see. Manifold looks good.
DME is requesting 17psi, only getting 2-3 psi.
Tried using an AEM infinity standalone also incase something wierd with the DME, same problem.
TPS adapt was done.
Not knocking, no misfires.
MAF seems to be fine (reading upwards of 700 HFM much less than i'm suppose to have.
Lambdas look good.

Any more brain storming would be appreciated.
Would BPVs cause this? They are open up to 5psi anyway on a normal car so the fact i'm not getting 2-3psi doesnt point to that.
I could have swore it was wastegates but if anything, if theres a problem it would be stuck closed not open.

 

BPV open to 5psi?! That doesn't sound right since it will bypass boost right bac into the intake. How exactly was the leak test done? Any possible intake restrictions? Recent work done?

 

Throttle body? I don't think that only doing the throttle position calibration will assure proper operation. Did you log throttle position? Although, a failing throttle body could potentially give a false position reading.

 

Logged throttle position and it reads 95%. I plan to take off the ypipe and compare it with the pedal position sensor.

I believe the BPV doesnt start to close till after 5psi? Correct me if i'm wrong but its normally open until boost.

Everything is clear intake wise. Leak down test was done multiple times by a shop that said there were some leaks that they fixed. I dont hear anything leaking also when driving.

 

Mine reads 99-100%. The difference between 95% and 100% in a butterfly valve like the throttle body has, would be negligible, but the fact it's not reading 100% might mean something.

Find out at what location the leak test was performed from. If it was done from the air box, a stuck open blow off valve won't be apparent. If it's done from the turbo outlets and holds pressure, the bovs are holding.

 

^^ test from the turbo outlet. The air is going somewhere and if the turbo spins freely and there's no exhaust leaks there's a boost leak for sure! Meanwhile know that you're working those turbos HARD and be gentle on them as they are almost certainly being oversped.

 

Any chance a catalytic is plugged?

 

Catalytic is not plugged, Took them out with the exhaust this morning to check the hot side wheel. Everything is fine. No play in the wheels and spins fine.

I will try testing from the turbo outlet and check the throttle body.

Throttle body from durametric is 99% using the OEM DME. I think I saw 95% on the AEM infinity which interprets the voltages of the TPS to show that value. Probably different scaling than stock ECU.

 

Easy to tell if your Diverters are working. Take them off and pressure test them if they leak then there bad. Usually if there bad you will have a Second air code fault because there leaking on first cold start up.

 

How did you pressure test? I always do post turbo on the output to intercooler hoses. Plug one side, add pressure rig to the other and the system should hold 20psi pretty easily.

The next thing to check is obviously your turbo blades both on intake side and exhaust side. However, when you check your exhaust side make sure your waste-gate flaps are in good working condition.

That all checks out look at your exhaust manifolds for exhaust leaks because if your not loosing basically all your exhaust you missed something or you have a problem that physics simply cannot resolve.



This type of failure is very very uncommon on a 996TT (I have never seen it)

 

Pressure tested at the turbo inlets, Dont hear any leaks,
Inlet Wheels are fine and spin freely.
Pressure tested the wastegates and they crack open at around 7-8psi which I what I expect from stock wastegates.
Exhaust manifolds look fine, no leaks that I can see.
Took off the y-pipe and the throttle plate opens and closes normally from pressing the pedal.

Wouldnt the diverters be ok if the pressure test can hold 25psi?

I'm really stumped on this.

 

Is it possible the MAP sensor is bad and the reading on the dash is incorrect? This is a real puzzle, it's like the car is corked up which is why I asked about the exhaust. Very weird...

 

Take your two diverters out. Hook up a hand pump on the nipple of each diverter. Pump it up and if you here and leaking there bad. I believe mine couldnt hold 6psi on one bov.


Map sensors do not go out often but you can clean it abd see. Hes not stumbling or hesitating so i doubt its that.

 

What kind of wastegates do you have? Less likely an issue on stocks, but check the arm to see if they are binding in any way through their motion of travel. It's possible they are binding open and not closing completely/easily.

 

The thing is I took the wastegate control out by removing the vacuum hose that goes to it. Then basically ran with wastegate spring pressure. If there was an issue it would be stuck close rather than somehow opening do to exhaust gas pressure. They are OEM wastegates.