83 fuel tank question

[boots]

My dad has an 83 CJ5 . It has a rebuilt AMC 258 i6 / 4.2l with Mopar fuel injection. We dropped the fuel tank yesterday because we could smell gas when parked if the tank was close to full. We had the tank half full and rolled it upside down and sideways and such and no gas leaked out. When I was taking hose off that goes to the fuel filter and pump, gas kept coming out of the tank as if it were pressurized. It sprayed all over the floor and me, then filled up a water bottle and was still going. My dad cracked the gas cap and it stopped immediately. After it was all back together I drove it to the store and when I got home I cracked the gas cap and it went woosh as a bunch of air came out. Is it supposed to be pressurized like that? Could the pressure be letting gas fumes out? It has the bigger factory tank if it makes ant difference.

Thanks for any help.

 

[bondo258]

Sounds like someone plugged the vent lines, vapor rollover/check valves, or vent line to the charcoal canister. Your fuel tank should not be pressurized. That is dangerous. You can run a vented fuel cap in the meantime, but that's not fixing your problem.

Vapor fumes are supposed to be stored in the charcoal canister, and burned off at times when the engine is running. That is for enviro, as well as gas mileage reasons. Evaporating gas costs you money. Using it in your engine, is what it's for.

If all those things were working OK and not leaking, you don't smell fumes.


Not sure how you dropped the tank without taking the gas cap off, the cap covers the neck mount screws to the filler plate, and the fuel inlet on the tank is above the frame. maybe it's not the right tank? Pics?

 

[boots]

Not sure how you dropped the tank without taking the gas cap off, the cap covers the neck mount screws to the filler plate, and the fuel inlet on the tank is above the frame. maybe it's not the right tank? Pics?

The tank was still in place when I disconnected the fuel pump and had to open the cap. But we were still able to drop the tank with out removing these screws your talking about. We just loosened the hose clamps on the tank inlets. The screw driver barely fit, but that's how I did it.


I drove the cj around today, I let it sit for about an hour before I put it back in the garage. It sat for another 15-30 minutes before I cracked the cap, nothing came out. Is it possible that the charcoal canister is old and just isn't absorbing the fumes fast enough? I'm gonna check for any suspicious looking hoses tomorrow.

Thanks
Chad

 

[bondo258]

When you had the tank down, did you notice two hoses going from the top of the tank (not on the fuel sender) going to a canister behind the left rear tire on the other side of your inner fender?

This is the liquid check valve. it is supposed to keep sloshing fuel from entering the vapor system in. It allows excess fuel to drain back into the tank. The tank lines connect to the bottom nipples.

This should be connected by a another hose, to the rollover valve, this valve keeps liquid from being forced through the vapor line if you roll over. A hose goes from here, to the vapor line that is metal, and the same size as your old fuel lines.

The other end of this line goes to a green plastic line, which should connect to your charcoal canister. your charcoal canister is located under the hood, beneath the brake booster.

A charcoal canister alone, won't hold pressure in your tank. Something is disconnected, routed incorrectly or plugged. Sometimes the metal lines can corrode on the inside, and get plugged, too.

To clean out a metal line, disconnect both ends and blow compressed air through it. Blow towards the engine.

Also the valve canisters are brittle and sometimes hard to find replacements. I'd cut the lines off and then slit them to peel them off, instead of pulling or twisting them off. It's worth taking your time on this step.

The charcoal canisters hose barbs can be brittle, too. FYI.

 

[boots]

The hoses were changed around when the injection was put on, but dad doesnt remember exactly what was done. The liquid check valve and rollover value don't appear to be there anymore. The two hoses on the top of the tank are connected via a Y fitting. From there they appear to go to the charcoal canister (im going to verify this tomorrow).There are two hoses on the sender. One is the pick up and goes the the fuel pump, the other is the return line. I'm going to check it out tomorrow and see if I find anything.

Thanks
Chad

 

[bondo258]

Good luck, and wear goggles if you try the compressed air trick.