JANE member Greeg Elevich writes

I am having a pressure buildup in my gas tanks, depending on
which one is switched on, in my 1986 XJ6. It is intermittent
and can occur after a few or several miles of driving. When it
really builds up, the car hesitates or stalls. When parked,
gasoline leaks out from the canister in the rf wheel well.

I suspect that the problem lies with the breather valve, but I
am wondering if anyone has experienced the problem and knows

Submitted by jam@ispwest.com on Mon, 12/27/2004 - 18:56

I think everyone has experienced that problem that has a Series 3 XJ-6 US Federal version.

Under the right front fender or "wing", (passenger side) you will find the
Charcoal Canister, a one-way black plastic Check Valve, maybe a second, 3-way black plastic Check Valve, and a number of hoses connecting to and from the Charcoal Canister, and one that connects to a steel line which crosses into the engine compartment and connects to (maybe) an electronic Solenoid Valve. Anyone of those parts could be causing the problem. The gas tank vapors are supposed to go through the first check valve, then to the canister, then through the second check valve, then through the solenoid, to be burned in the intake manifold.

TEST: remove the first check valve, it has two different diameter hoses attached to it; Go to the auto parts store and get a straight-thru plastic connector that accepts different diameter hoses on each end, then connect both hoses (without the check valve). See if that does it. (it fixed my problem). If so, the first check valve is bad, it is a General Motors valve by the way.

The leaking occurs when the tank expands with vapor and spreads the seams, if you don't correct the problem, you'll need a replacement tank soon.
When tyou open the filler cap, the vapors swoosh out and the tank contracts
back to shape. the expansion-contraction destroys the seams. Hopefully you might stop the damage temporarily with a straight-thru connector until you get a new check valve.

When you get the new check valve, take a 1/8" drill bit and insert it in the valve until you hear a "pop", that means the valve is now "Primed",
(just joking, but serious), if you don't "prime" it, you'll be back in the
high life again...