Boost leaks
 

Hi!

I have a problem on my 2.7t A6 APB.
One day I had a loss of power and weard noise (whistling) - don't think thats a bad turbo as there is no smoke and I have checked turbos from exhaust side - center is in perfect condition - no movement (checked during downpipe gutting). So I decided to make a boost leak test - I doesnt hold any boost and as I noteced boost is going out to oil catch cant that is vented to atmothfere (y-pipe is cuttet off). Antifreeze level is ok, no oil in it. Should those be bad rings in cilinders or turbo cartridge - have can boost get in sump or cylinder heads? Also noticed that my oil catch can is full of water (tea color, yellow) - it can get half full ~200-250ml in one week (~400-450km). F hose is deleted.

anyone?

1) i disconected n75 cable - max boost i get is 0,3bar
2) i disconected diverter vaslves (bypass) - no changes - 0,3bar
3) i plugged off n75 pipe from turbo housing - driving very careful - boosted 0,8-0,9bar and could boost even more, but didnt want to blow turbos.

Your going to just have to get in there and look. The rubber coupler that the 2 pipes go into the throttle body is a common one. The rubber connections at the intercoolers can come off also.

All pipes are silicone one, except of rs4 y-pipe.
checked those - no leaks, I have two clamps on throttle for safety :)

starting to thing that problem is underneath - need to make smoke machine ,to do proper test. I hope that turbo cartridge is ok an there is no boost going in oil system.

If boost is going into oil system you will always notice your dipstick has blown out when you pop your hood.


I did a boost leak test on an AEB Audi and found the false air coming through the valve cover gasket...


also, make sure all your check valves are good. Common failure on turbo cars. Sometimes people install one way valves backwards and f everything up.


also, check the wastefate diaphragm. I see those go bad on Volvo TD04h turbos a lot.

I have open type ventilation with oil catch can so it cant make any boost inside and blow out dipstick. All the check valves are cut out including n80. So I did the boost / smoke test - there is smoke going out of head and crank ventilation (cylinder heads and block) + there is little smoke going out of n75 nipple that vents to atmothfere. I blown 0,5bar in system and it hold only 12 seconds until it drops to 0 bar (hearing bubbling sound). N75 measures 30,2 omh. Still strange whistele sound at boost.

So i got n75 from 1.8T for test it is boosting a little better in beggining vas 0,6-0,7bar, but now onli 0,6/0,6bar (don't know why). Now looking to buy oem 2.7t n75.

Here's im thinking...

You stated that when you pressurize the system, it takes 12 seconds to lose all the pressure. That being said, the car should spike boost, and taper as it leaks (while driving) Like if you do a WOT pull. If its at stock boost, it should build 11psi, and then start leaking off if its a good leak, not just a pinhole.


Idk man, its hard to diagnost over the Web, but here are some suggestions:

Test wastegates. If you have only oene bad wastegate, it could be the reason why you have a low boost condition.

Pressureize the system with your boost leak tester, and use soapy water to spray around to find the leaks. ALL the leaks must be sealed in order to further diagnose a driveability condition. Even if you have a leak coming from the camshaft seals, or leaking through an injector o-ring.


Another thing to think about is, if you have any Check Engine Light codes, it would be a good idea to diagnose and repair accordingly. Like if you have a MAP sensr circuit code, The computer might be cutting boost to keep from engine damage. If you have a faulty MAF reading, it could cause the computer to also cut boost.

These are just some ideas to think about while trying to figure out what is wrong with your car. Hope this helps, Connor.

Thanks for advice. There were a lot of errors in vag scan (as I havent deleted them for a while). Now there ar two left:

2 Faults Found:
17834 - EVAP Purge Valve (N80): Open Circuit
P1426 - 35-00 - -

17522 - Oxygen (Lambda) Sensor: B1 S2: Internal Resistance too High
P1114 - 35-00 - -

N80 is deleted so..

Ok. Now I have also changed B1S2 lambda sensor - it didnt have any resistion (omh), no codes bor rear lambas. But now i got resistance code for both B1S1 and B2S1 :@ I measured resistants - it was ok - for one 10,5 for second one 13 omh, so heater is working. Car is also acting strange sometimes it boosts 0,6/0,7bar, sometimes o,5bar. Not sure if its from temperature or something.