Hello, I have a 1983 XJ6 that sat for about 3 years while I was stationed overseas. When I got back I drained all the fluids including gas. I then replaced the fuel and fuel filters. The new problem I am having is that the passenger tank has gas bubbling in the neck of the tank and it is over pressurized and fuel flows out the cap if opened. This happens even if the car is not run and is just sitting over night.

When I open the cap slowly to release the pressure I can hear the tank contracting back into shape, bad I know. Could a bad charcoal filter being causing this or is there a pressure relief valve anywhere? Also it appears that all of the fuel is going into the passenger side tank? Any help with this is greatly appreciated. Thank you,

 

There are a couple pressure valves in the vent and cannister system.

If you look behind the right front wheel you'll see one of them with vacuum/vent hoses running horizontally. Remove the aft-position vent hose from the valve. This is the hose that goes to the tanks. With it removed the tanks now vent to atmosphere. Give it a whirl and see if your venting problem goes way.

It also sounds like you might have a problem with the fuel return system where fuel is drawn from one tank but returned to the opposite tank...causing the opposite tank to overfill. This would be a return valve problem.

But open the tank vent as described above, see if anything changes, and we'll go from there

Cheers
DD

 

like Doug says, try the Pressure Release Valve first;

it's a black plastic GM valve and it looks like the picture below. Located between two gasoline vapors rubber hoses, themselves attached with clips to the inner fender wheel well; If you follow the "exit" hose (after the valve), it connects to the Charcoal Canister, which itself is located in the front fender wheel well behind the passenger side headlamp.

remove the valve and pierce the membrane inside pushing a 1/8" drill bit through it and pulling the bit from the other side; This has been a known issue with these cars since the 1980's and the fix is to either pierce the valve or remove it entirely by installing a hose-to-hose splicer. Notice that the valve fits the hoses one way only, one side has a bigger hose than the other. The problem is the valve's calibration, it requires too much pressure to open, so replacing the valve does NOT fix the problem.

you will have to raise the front passenger side of the car to see the valve.

 

Thank you for the quick replys. I pulled out the valve and ran a drill bit through the valve so it could no close anymore. Started up the car and it ran pretty good on right tank. When I switched to left tank, it started running really rough. I tried to give it some gas to keep it ideling but it was extremely rough and died. When I got out I noticed a ton of gas coming out of the charcoal filter? Any other ideas on what is going on?

 

Sorry above post is confusing. Ran ok on driver side tank (US driver side) passenger side is having the issues. Thank you,

 

Are the tanks full?

Perhaps one tank is over-filling and the excess going into the cannister.

Select the right tank, run the engine, and look inside the fuel filler neck. Might need a flashlight. Do you see a small stream of fuel running into the right tank? If so, good. If not, see if "return fuel" is going to the left tank. If it is, it shouldn't be.

Now repeat the test with the left tank selected.

There are other possibilities but I'd start the investigation here.

Cheers
DD

 

The mechanic who lives next door to me said that he full drained both tanks of old gas. We put in 3 gallons in passenger tank and 2 in driver side tank. When I look in the passenger side tank the fuel is up to the top of the neck and it is still bubbling a little but not as bad as it was before. I am going to try to get it running again so I can see if the fuel is returning. But if I remember correctly there was fuel returning to both tanks at same time through a little hole at the top of the fuel tank neck when the driver tank or passenger tank were selected. Thanks for your help on this.

 

there should not be any liquid fuel running through the vapor line from the fuel tanks.

the problem is obviously elsewhere, the piercing of the pressure release valve does not cause liquid fuel to come into the vapor line, it just allows the vapor pressure to be released and eliminates the vapor buildup that was expanding and contracting the tanks. One problem is already resolved, now we have to find out whiat is causing liquid fuel to travel to the vapor release line.

is there gasoline leaking anywhere else? inside the trunk? under the tank? Was the fuel filter replaced by the mechanic? could the fuel filter lines have been inverted?

it is starting to sound like one of the Return valves is bad. Attached is a WORD file with tips to troubleshoot the fuel changeover system. I hope it helps.

 

Thanks to your help I am making progress. I drained about 3 gallons from the passenger tank and added it to the driver tank. It seems the passenger tank was just way over full, not sure how as I only put 5 gallons into the both tanks. Must have not drained completely. Now I can get the car running and it idels really smooth on either tank. after about 10 minutes it starts ideling really rough and dies. I did add some injector cleaner to hopefully clean out any varnish in the lines and tanks. I cannot tell if the unused fuel is returning to the correct tank. Should I see it coming out at the little hole at the right above the spring door at the fuel neck? Or is the return below the spring door? Thank you,

 

take a long screwdriver, insert it down on the filler neck to push the spring door open, then look down with a flashlight, you should see the flow of gasoline in the selected tank. (engine running).

**make sure the screwdriver handle cannot go through the filler hole, in case it falls off your hand, you don't want a screwdriver falling inside the tank!!

the rough idling could be the O2 Sensor needs replacing or the Coolant Temperature Sensor, (you only have to replace those once during ownership of the car).

Before you replace the O2 Sensor, get a length of insulated wire, as thick a gauge as you can find; Remove 3 inches of insulation on one side and ½ inch on the other;

with engine cold, wrap the 3" inch side tightly around the O2 sensor's metal body; Run the engine and touch the other side of the wire to a good clean chassis bolt; ( Do not touch the O2 Sensor, it gets extremely hot and will burn you after 1 minute of idling).

see how it idles with and without touching the ground wire to a bolt. If the idling improves and stabilizes when wire is touching a bolt, (O2 sensor being grounded), you need a Ground Strap for the O2 Sensor. I made one for my 1984 and it improved things 100%.