Re: more on the Fog Horn

[steveb@falcon.kla.com (Steven Buchholz)]

> You may recall my post from a month ago... I reported a fog horn type =
> sound from the rear of the car. Dealer thought it was the conveniance =
> (power locking) package and replaced the pump. Guess what, that wasn't =
> it.
> 
> As a reminder there is a cyclical (on for 8 seconds, off for 20) type of =
> hum from the rear of the car on particularly warm days (80 F). On cooler =
> days there is no sound. The sound usually is heard after shutting down =
> (such as coming home from work), although has occurred when the car is =
> under way.
> 
> Does this symptom sound familiar to anyone? Past discussions suggested =
> the fuel pump as the culprit. Dealer says this may be so, but since the =
> sound occurs when shut down, he's suspicious... By the way, where is the =
> fuel pump... If I could put my ear to it while the noise is occurring, I =
> might be able to confirm one way or another.
> 
... I am not at all familiar with the fuel system in the newer Audis, so I'm
sorry that I can't help you there.  My infamiliarity makes me also offer this
as a suggestion for something to look for, I don't know if it is even poss-
ible for the car, but based on your description, I'm betting that it is fuel
vapor.  The fuel system is supposed to be sealed, but there's probably a 
pressure relief valve that vents to the recovery cannister, you may be hearing
the relief valve actuating.  I have such a valve on my K-bike, and it usually
works when the engine is shut down.  It does make a noise similar to the one
you describe ... I call it the "mating call" of the k1.  It may be true that
your car doesn't have such a valve, then it may be simply a bad seal at the 
fuel cap, or perhaps a crimped vent line.  A real easy test would be to pop
off the gas cap while it is cycling and then see if the noise stops ...

HTH!
Steve Buchholz
s_buchho@kla.com

Hey, if this works can I send a copywrited [sic] version to QCUSA to be 
included in the Q^2?  ;-)