i have a 2000 a6 2.7l with an apr computer which i was told should putt out 14.7 lbs of boost. my question is, when it initially boosts it goes up to 15-17psi then gradually the boost lowers to around 10psi as the rpms increase. it seems to start losing boost after 3000-3500 rpms. it seems to level off at 10psi, is this normal. I bought the car with the computer done already.the rest of the car is stock as far as i know. i have checked for boost leaks and codes. no leaks or codes. just wondering if this is normal or what i should check or replace to keep boost up.

 

Sounds like one or both of the turbos may not be producing full boost, possibly due to a slightly leaking wastegate. This would show up at higher rpms when the engine needs more airflow, and the leaky wastegate makes the turbo produce less than full boost. Since the leak is on the exhaust side, and down the tailpipe, you never see or hear anything. Maybe a bad/stuck N75 valve, which controls the wastegates...
Jim

 

it seems to produce plenty of boost to start with, around 17psi. how can i test to see if the wastegate is leaking. or if the n75 is working improperly. thanks for the reply.

 

You can test the wastegates by disconnecting / blocking (both ways) the atmosphere connection on the N75 valve (the one that points toward the passenger front wheel) and CAREFULLY see what kind of boost you can develop. Just be really careful - you now have no boost regulation at all, except for the overboost cutoff. Just don't mash the pedal and hold it WOT, and I'd only do this with a known calibrated boost gauge right in front of me...
If you can get higher boost this way, then the N75 is leaking. If it still goes down, then you've got either a leaky wastegate, a leaking hose from the N75 to the wastegates, or a turbo that's not making boost for some other reason.
Jim

 

thanks for the info. i will try that. i will be very careful when testing.

 

Could it be a diverter valve or throttle body boot? I was told they had to be beefed up before chipping. Poster stated rest of car was stock.

 

TBB will show up with a leak test. DV is a possibility, if one is leaking, but at a given boost pressure the boost should still go up with increasing RPM, as the leak gets overwhelmed by more airflow from the turbos. That's the reverse of what he's seeing...
Jim