Well, my car has all sorts of little fuel issues, but two that have been bothering me the most lately are thus:

1. When I fuel up with the engine hot (after a trip or something) after the pump shuts off (first time it shuts off) if I remove the nozzle and let the car sit a minute or two, gas comes gushing out of the filler neck. I think it might be my return line, but honestly, I don't know. I lose quite a bit of gas this way. Could this be my FPR?

2. I hear the "bubbling" noise coming from my gas tank at shutoff. Some say this is due to the charcoal canister being clogged, others say it's the UFO on the bottom of the tank. Which is the best to check, and how?


Oh! And when I first bought the car, it would never fill up right. If the pump was at full speed, it would shut off four or five gallons early, so I either had to fill the car slowly, or keep filling it after it clicked. A friend of mine has the same problem. What causes this?

 

I've seen this before, on a '78 El Camino. A previous owner had cut the tank filler neck off and replaced it with one from a different vehicle.

It may be that a previous owner cut the neck to drop the tank. Even if the original neck is used, it isn't right. Slide under the rear drivers side and look at the filler neck. Stock was a solid neck, no rubber coupler. If you see a rubber coupler. . .

RBob.

 

No rubber coupler. Just poked around under the rear of my car for a good half hour. Everything under there is factory stock. Springs with the part number tags, shocks, crappy BW 9 bolt, exhaust, heat shielding. The whole enchilada.

The little UFO seemed easy enough to get to, might try replacing it for giggles. If that doesn't work, I guess it's either the pump, charcoal canister, or the FPR. Not much else in the system that can cause the tank to overflow.

What about the "hard filling" issue? I'm guessing this would be related, as it seems to have to do with too much pressure building in the tank.

 

It is strange that after a fill up with the cap off fuel spills out the neck. I'm thinking that with the cap off no pressure can build up. So why the fuel spill out the neck? It may be that some of the lines from the tank are not connected properly. Or, is the car sitting level when being filled? If not that may be an issue.

If I am not understanding, and the cap is back on, then after a minute the fuel spills out: The proper cap does not have a vent, it is a solid seal. And/or, it may be the UFO (which vents in/out at a psi or 2) is bad. Or the CCP line from the tank is plugged.

HTH's,

RBob.

 

No, cap isn't on and fuel comes out. Car is level.

 

I think I have part of your problem.... Most gas stations around here, (Mass), have nozzles that don't fit into my filler tube quite right, so I have to angle the nozzle upwards to keep the pump from shutting off due to tank pressure buildup. Thats part of the nozzle design...to automatically shut off the pump if the gas tank gets too full. Maybe you are facing the same issue, but the stupid pump isn't working right?

 

Hmm. I don't know.

Just figured something else out today. It seems that my gas tank pressurizes abnormally. As in, I took the cap off, and it kept pushing out gas fumes for like ten or so minutes. Don't the fumes vent into the charcoal canister? So that must be clogged up, or something. I have this feeling I'm gonna be fighting this fuel problem for a while. >.<

 

Yeah it should not pressurize like that. Definately check out your charcoal canister for oil sludge build up and run a small "snake" or a thick gage wire through the return line.Work it through slowly and do not force it. If you hit a blockage, turn the wire and see if you can work your way gently through the blockage. It may take a while so be patient and be careful to not have the wire break off inside the return line. Good luck & Keep me updated

 

I think I'm missing something here but, here's my opinion anyway:
The filler neck should have a vent tube in it to allow air to escape from the tank while you are filling. If that tube is missing or pinched, it will cause the pump handle to shut off while fueling even if you're not full. I would check that first for a slow fill condition.

I suppose that, if you didn't have that vent tube, you could possibly trap some air in the tank. When the trapped air heated up (heat from the exhaust) it may push gas out of the filler.

 

The problem is the muffler. It dates back to 1986. Here's a blurb from the 1986 Firebird data:
If you have enough horsepower under the hood and a non-stock muffler (like Flowmaster, others are similar) it will heat the gasoline in the tank too much causing it to boil. Ethanol makes this problem even worse.
Flowmaster finally sells an additional bolt-on heat shield for their mufflers...

 

Nah, thats not it. The muffler doesnt blow off enough heat to heat up the fuel like that and vaporize it. Vapor lock is caused by superheated fuel in a fuel line, not tank. The air bubble formed causes the mechanical pump to no longer pump fuel and you get a car that wont start.

Probably your vent line is clogged/blocked. The only vent runs to the charcoal canister, so start with that. May even have a kink in the metal line somewhere. Try running some leaded fuel.

 

And clog up my cat worse than I'm sure it already is? Don't think the O2 sensor can get any worse though. :P I gatta get under this thing. Stupid apartment complex and their, "no working on cars," policy.