need help with misfire on my 2.7t c5

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07-26-2014, 05:05 AM

#21

Gsrob

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Quote:

Originally Posted by vtraudt

Your 'squeaking' sound caught my attention. Currently chasing the cause on my 2002 A6 2.7T.

I called it a 'mooing' sound. Occurs when boost is building (I have larger turbos, etc.).

I got rid of a similar sound on B6 A4 1.8T with APR R1 (bladder type) DV by changing the orientation of the DV. After that success, I did the same on the 2.7T (Forge=piston DV), but no change.

Today, I have a 'smoker' here to see if I am dealing with a boost or vac leak.

I am confident that mine is not the DVs. A couple of months ago I purchased and installed new oem 710ns and made sure I installed them according to factory spec (ie correct orientation) since I read that they would make squeaking/whistling/honking noises if installed reverse. I also replaced a variety of hose clamps that were absent from the vehicle when I first purchased it back in November. Let me know how the smoke works out. I have toyed around with building a pressure tester as seen at JHM for the S4 or other places. OP - Maybe you could do the same to check for a vacuum leak?

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07-26-2014, 05:31 AM

#22

vtraudt

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Squeaking Mooing Sound

Quote:

Originally Posted by Gsrob

DV orientation: There is an Audi way (pressure coming in from the side) and a 'normal' way. I read that Audi back when used the normal way, but had problems with their plastic rubber bladder 710 (A, B) DV. Turned around and seemed to work. The logical way is to have the pressure face the the bottom 'piston'. I have run them both ways, no difference with the exception of the noted B6 1.8T APR R1 bladder valve. Mooing installed the Audi way, not mooing the 'normal' way. Valve had been sent to APR for rebuild. We now doubt that new parts actually went in. Will replace today with my Forge clone on that car.

Pressure test (Home depot plastic plumbing section, hose clamps, compressed air connection, pressure reducer/gauge) on 2.7T after smoke test today.

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10-14-2022, 05:30 AM

#23

JG27

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Quote:

Originally Posted by Gsrob

Pre-cat O2 sensors can and will cause your engine to misfire. I searched high and low for what was causing mine at the time and finally narrowed it down to the pre-cat driver side O2 after many people posted that an O2 would not cause those symptoms. Are you getting a flashing check engine light while driving? If so, don't. I'd probably start there since you are dealing with a random misfire on top of cylinder 5, but others with more experience may have greater insight based on the EGT code you're getting.

How to enable misfire logging? Years ago could read them on vagcom, but cant do now.