heymoe

I have a 2002 (C5) A6 with a 2.7T engine. I've been noticing for a while now that after I fill up with gas and between 3/4 and full tank (about 100 miles) that my car will go though moments of hesitation / loss of power while driving at any speed (city or highway) and rough idle if at a stand still. The car has stalled a few times at a stand still but that doesn't happen often. When it does happen at highway speed, the loss of power if jarring and not like lifting off on the gas pedal quickly.

Now this doesn't happen after every fill-up but if it does happen it's always within that first 100 miles after fill up. If it does happen, it will go on and off for a few mins then then things go back to normal.

No codes are being thrown which isn't helping debug the issue with Audi Service and of course it never happens when they are taking it for a test drive. We have tried / tested the evap purge valve but it has tested OK and we even clamped it off to makes sure there is no leaks but the issue still happens. The tech said it could be the fuel pump but I would think it if was the fuel pump that I would have had the issue happen at anytime after a fill-up and not just the first 100 miles but who knows.

Does anyone here have an thoughts / ideas of what might be going on or recommendations of something else to try / test?

Thanks in advance for any feedback.

-Gary

georgeb944

Do a smoke test for a vacuum leak / boost leak.

clancy

When is the last time you changed the fuel filler cap? I am told while this is a rather generic part it is still best to pay the bucks for OEM and be sure it is specific to your VIN. There are several iterations.

heymoe

I'll mention the smoke test to my tech the next time I have the car in though if it is a vacuum / boost leak, I would think the issue would happen at any time and not just 100 or so miles after a fill-up.

I did replace the gas cap with an OEM one back in 2013 due to a broken tether. The issue didn't start after the cap was replaced but I guess the pressure release valve in the cap could have failed or something. I don't hear any pressure release when I remove the gas cap though. Any ways, I'm pretty sure I still have the old gas cap that I can try using again.

Thanks for the feedback so far.