Gas gushes out of gas cap after a fill-up

[Theodore]

Have had our ‘90 Wagoneer since August, but between not running right & being in the shop, yesterday was the first time i had to buy gas.

At the pump, when i opened the cap, there was a slight rush of air as pressure/vacuum? released. i filled the tank til it clicked & thought it be a good idea to add fuel injector cleaner.

So we ran down the road a mile or so to the parts store & got some. When i opened the cap this time, about a 1/2 pint of gas shot out under pressure. Have never seen anything like this before.

Is there a trick to open the gas cap to not get wet with gas? Or, can i only run the tank 3/4’s full?

Here’s pic of the gas cap we have.






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[mx71]

Have a look at all your gas tank vents/vent hoses. Something isn't working right. Could have sat for a while and have gelled fuel in one of the lines.

[letank]

disconnect the gas tank vent at the charcoal canister, to see if it alleviate the pressure issue... something is not venting

[tgreese]

If the '90 is like the rest of the Jeeps over the years, the TSM will have a detailed drawing of the fuel tank and its plumbing. There is an '89 TSM on the Tom Collins site that may help you - http://oljeep.com/edge_parts_man.html

I recall the fill hoses for these GWs are skinny and long, and you may need to adjust how they are hanging. I'd think you'd need two things for gas to come spurting out - a local low spot in the fill hose where gas pools, and second some build-up of pressure in the tank that forces that pool of gas back at the fill port. The vapor recovery system is supposed to vent the tank to the atmosphere, but if your charcoal canister is plugged up, or if it's been removed and the lines capped, the tank will not be vented. Vapor is supposed to go out through the charcoal bed (where it is absorbed) and fresh air come back in. The tank is open to the atmosphere except for the fuel-scavenging charcoal screen in the vent's path.

[candymancan]

My 90 gushes a little air out sometimes when i open the cap.. but never had gas gush out before

[Theodore]

Thanks for the replies. Looking around this morning, I noticed a couple things:
1) the evap canister is gone;
2) the 2 lines that go to the gas tank are capped off

Have seen comments elsewhere on the forum re: either using a vented gas cap, removing the gasket from the non-vented cap, or adding a fuel filter at the end of the line to enable venting without enabling dirt/moisture to enter the system.

I'd prefer not to go the vented cap route, so am thinking I'll go with adding an inline fuel filter to the line, until I can do something permanent. Am wondering what other issues will be caused by going this route vs. replacing the evap canister.

[tgreese]

Correct, the gas tank needs a vent to both accomodate the changes in vapor pressure with temperature, and to allow air into the tank to make up for the fuel volume that's drawn out as you drive. Too bad the vapor recovery system is gone. They have no effect on performance, minimal maintenance and vent your tank without any odor. Besides keeping the atmosphere cleaner. IMO it's just wrong-headed to remove them. You can put the tank vent part back if you want ... the tank vent part is quite simple.

With either a vented cap or a remote vent, you'll probably smell gas, especially if you park the Jeep in a garage.

[mx71]

You can use an EVAP canister off a ZJ.

[candymancan]

I have a vented cap on mine... It just a basic gas cap from autozone that poped up when i gave them my make and model... Im pretty sure they all have some kind of pressure release on the caps.

Tbh im not worried about the air coming out of my cap its just a quick woosh sometimes not all the time.. Its usually when the tabk is about half empty or near empty and been driven for a little bit. Now if i had gas woosh out lol sure

[Renodemona]

Run at least one vent line, there should be a metal tube that sticks down by the left rear wheel arch that runs up to the vent on the inside of the gas fill port that is easy to connect to. If not, you can run some line up over the top of the spare tire area to vent up by the tailgate. Just make sure its pretty uphill from the tank. That gas cap might be making too good of a seal as well I had a similar issue with a locking gas cap on my J truck. Good luck!

[Theodore]

Took a while, but i was finally able to permanently solve the issue, by adding back the charcoal canister, replacing associated fuel tank vent & vacuum lines - post w/details & part numbers is here: https://www.fsjnetwork.com/forum/viewto ... 51#p208851