Fuel Tank Overpressurizing

[91waggin]

So here's what's going on: After I fill my tank, I'll drive for a couple miles, and then I'll start smelling gas. I'll go back and look at the gas flap and it will have sprayed fuel all over the place inside the filler flap. I'll pull the gas cap off and a whole bunch of fumes will vent out like the fuel tank is under tons of pressure. But then it won't happen again until I fill the tank again.

Are fuel caps meant to vent pressure at a certain PSI like radiator caps? I'm not sure, but I'm fairly sure that the tank is overpressurizing, rather than the cap being the issue.

Any thoughts?

[Lincolnmania]

check the vapor return soleniod

[91waggin]

Is that the one over between the battery and the fenderwell? Two prong electrical, two rubber hoses, one of which goes to the upper intake? How do I test this?

[Lincolnmania]

yes
put power to it and it is supposed to not hold vacuum

[cld783]

Is that the one over between the battery and the fenderwell? Two prong electrical, two rubber hoses, one of which goes to the upper intake? How do I test this?

yup..

i'm guessing you should be able to apply voltage to it and see if it opens and closes properly... or you could just stand there with your ear up to it and listen for a while

I may be wrong but i believe our gas caps aren't meant to vent, thats the job of the purge solenoid.. it sucks fuel vapors into the intake where they can be burned, so you either have a solenoid issue or a clogged vent line..

[91waggin]

I may be wrong but i believe our gas caps aren't meant to vent, thats the job of the purge solenoid.. it sucks fuel vapors into the intake where they can be burned, so you either have a solenoid issue or a clogged vent line..

Chilton's says this:

Pressure Vacuum Filler Cap

The fuel cap contains an integral pressure and vacuum relief valve. The vacuum valve acts to allow air into the fuel tank to replace the fuel as it is used, while preventing vapors from escaping the tank through the atmosphere. The vacuum relief valve opens after a vacuum of 0.5hg. The pressure valve acts as a backup pressure relief valve in the event the normal venting system is overcome by excessive generation of internal pressure or restriction of the normal venting system. The pressure relief range is 1.6 -2.1 psi. Fill cap damage or contamination that stops the pressure vacuum valve from working may result in deformation of the fuel tank.

What I figure that to mean is that if the solenoid quits, then the gas cap will vent (albeit rather stinkily and messily) and prevent the fuel tank from blowing up under excess internal pressure.

[cld783]

thats good to know.. I knew it had vacuum relief but i wasn't aware it had a back up vent.

do you top off your tank alot??

[91waggin]

No. I run it down to about a quarter and fill it up. I commute in this car, about 20 miles one way.

[91waggin]

I replaced the purge solenoid and the gas cap. It worked fine for 5-6 tanks of fuel and now it's doing it again. I haven't verified whether the solenoid actually works, but it seems as though it does, since I got almost no hiss every time I pulled the gas cap until recently.

[Nathan in MI]

Did you verify that the hoses running to the purge solenoid aren't plugged?

[89LincolnTWNcar]

I have a problem where I can't add fuel too fast or it will choke on itself and spray out everywhere...its lame

[91waggin]

Did you verify that the hoses running to the purge solenoid aren't plugged?

I will add this to the list.

[Lincolnmania]

the vapor line is 1/4 steel and might be rusted shut

[91waggin]

the vapor line is 1/4 steel and might be rusted shut

The vapor line is the one running from the fuel tank to the canister? Forgive my ignorance, I'm not very familiar with the system.

[gadget73]

yes, its the small steel line from the canister back to the tank.