Pressure build up in fuel tank, 5kcstq

[Fred Munro]

Hi DeWitt;

Every Audi I've owned has had a pressurized tank - I think it's normal. You
may have a problem with the charcoal canister, though. AFAIK the charcoal is
supposed to absorb the gas vapour and then release it via air stripping when
the engine is running. Maybe your charcoal no longer absorbs the vapour or
the canister is plugged.

Fred Munro
'94 S4  121k km

----- Original Message -----
From: "DeWitt Harrison" <de at aztek-eng.com>
To: <quattro at audifans.com>
Sent: Wednesday, January 10, 2001 12:39 PM
Subject: Pressure build up in fuel tank, 5kcstq


> When I open the gas cap, I get a little rush of air indicating there
> is positive pressure in the fuel tank. This has been going on
> for so long, I can't really remember if it was ever greatly different.
> The engine idles and runs well. Now, however, the pressure
> is apparently sufficient to push fumes past the gas cap seal
> and I get gas odor after stopping the car. No fuel leaks
> found after a thorough inspection.
>
> Significant improvement was realized by adding a thin rubber
> washer to the gas cap seal but I believe I'm still getting gas
> smells from somewhere. This suggests to me that something having
> to do with the tank ventilation system is plugged. So far I haven't
> been able to locate a blockage. At least a small amount of air
> will pass though any hose I blow into including most of the
> charcoal canister plumbing. Charcoal canister solenoid
> operation also verified. Do charcoal canisters become blocked?
>
> Does this scenario sound familiar to anyone? TIA.
>
> DeWitt Harrison
> Boulder, CO
> 88 5kcstq
>
>