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Pressurization in gas tank on VR6?

I have a 1996 Jetta GLX (VR6, 85K) with a sporadic failure in the EVAP emission control system. To try out one possible fix, I just put in a new VW gas cap, since a VW dealer parts guy (whom I respect) said that most aftermarket caps won't do a good enough sealing job on the gas tank. When I put in the new gas cap, I noticed that the "pressurized" sound of that little valve on the side of the tank inlet (near the cap) didn't occur. I used to be able to push that thing and hear a "pressurized" sound coming from it (like an open tire valve).

My question is: what causes that pressurization in the tank?

I am guessing that if the new gas cap doesn't solve my problem, it could be whatever causes that pressurization in the gas tank. Anyone know?

TIA, Bob

Reply to
Bob Navarro
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You may very well have a vapor leak in the EVAP system.

Reply to
Woodchuck

If it is a vapor leak in the EVAP system, how would I diagnose it further? Or am I pretty much at the mercy of the dealer? (e.g., smoke machine or something)

BTW, I listened to the purge regulator valve at idle (stethosc> You may very well have a vapor leak in the EVAP system.

Reply to
Bob Navarro

Without having a way to scan the codes and start the diagnosis to run the pump to test the system it's kinda hard to do. But I can tell you this 90% of the leaks is caused by the evap tank located under the right front fender liner. It has a electronic valve at the bottom that goes bad but you must get the tank to get the valve.

Reply to
Woodchuck

Thanks. That's the kind of info I was looking for (i.e. based on others' experiences). I assume you are talking about what the Bentley manual calls the "charcoal canister", right?

Thanks for the help, Bob

====== Woodchuck wrote:

Reply to
Bob Navarro

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