I have an Audi A6 2.8 Avant 1998, U.K.
My problem is when the car is running, the fuel pressure in the tank gets so high you can hear air hissing out of the filler cap area. I can fill up with fuel as normal and apart from the fuel level indicator being a little erratic the car is running OK and has been with this problem for over a week.
Any thoughts? A simple case of replacing the fuel pressure regulator?







I.T.

 

Have just checked car again, and it appears to be pulling a vacuum from the filler cap rather than pushing air out...

 

Turns out replacing the following parts fixed the problem
4B0 201 803B CARBON ACTIVATED CHARCOAL CANNISTER
077 133 517 C EVAP PURGE VALVE