Hi, my name is Keith and I recently bought a 1976 f150. It has duel gas tanks and a 390 big block motor. I recently started having a problem, the fuel tank is building up so much pressure it is pushing the gas back up and pushing it past the gas cap and spilling it on the ground. I believe it does not have a EEC fuel tank. I am not sure if the gas cap I put on is a vented one or not. And also not sure if the truck is suppose to have the charcoal canister. I can't figure out why it's building so much pressure, if anyone has any advice it would be greatly appreciated. Thank you.

 

Welcome to FTE

Without Evaporative Emission (Evap/Em): Vented fuel cap.

With Evap/Em: NON vented fuel cap.

If Evap/Em present, tank has a hole adjacent to sending unit for fuel vapor valve.

Lines routes along right inner frame rail from valve to charcoal canister under the hood, located either below the alternator on the frame rail or in front of it.

But...since the problem began recently, it may have nothing to do with the fuel cap.

You live in Arid-Zona, how hot is it in Phoenix? I think I read in the LA Times that it was 112 yesterday.

Heat causes gasoline to expand, fill the tank all the way up, some will leak out. Very common for this to occur on these trucks.

 

Do you know where I can find a vented gas cap? I been to a few different auto parts stores and every time ask for a vented cap they bring something different every time.

 

Are you SURE you don't have Evap/Em? Fuel cap is an oddball with Evap/Em, non vented...has 4 prongs, 2 above, 2 below 180 degrees apart.

Fuel filler tube has a restrictor inside that only an Evap/Em cap will fit into. Evap/Em: Unleaded fuel only.

Without Evap/Em: 2 prong vented cap, no restrictor inside fuel filler tube, leaded fuel.

Back then there were two different sizes of gas station nozzles, two different types of gasoline, leaded and unleaded.

Lead in gas caused charcoal inside canister to melt (ditto in catalytic converters). Leaded gas station nozzles larger, would not fit inside restricted unleaded fuel filler tubes.

 

Yeah I'm sure. The gas caps on mine are two prong and inside the filler tube it's wide open. I also went out and looked there is no charcoal canister and I didn't see any extra lines coming from the tank that looked like they would go to one.