I'm new to Fords and to this forum, and I could really use some help. I recently bought a 1986 F150 4x4 with the EFI 302 motor and dual gas tanks. When I bought the truck, the guy said that the front gas tank didn't work. I have verified that gas doesn't leave the front tank, and when I select the front tank, the gas gauge reads below empty even though the truck runs fine. When I changed the fuel filter (canister type), I realized I only had three of the four fuel lines from the tanks connected to the fuel filter assembly, and two lines going to the engine. It looks like the fourth fuel line should connect to the filter assembly. But it looks like someone used JB weld over the connection. Does the canister type fuel filter assembly have four lines connected from the gas tanks or only three? Any help would be appreciated.

 

I'm guessing here, but I think that the two lines going to the tank are fuel / vent. I know that when you loose a pump in one of the tanks alot of times they'll cross feed and you spit fuel out the non-working tank filler. Maybe that's what was going on but rather then fix the pump they just blocked the vent?

I believe that the selector switch is pressure operated. So when you switch tanks you're really turning off one pump and turning on the other. The differnce in the pressure causes the valve to switch positions. When the pump goes bad the valve doesn't fully switch and I think that's what causes the crossfeed.

My guess is that you have a bad in tank pump. Also with the selector messed up you'll need one of those and possible the line to the tank if it's not there.

You can check for voltage at the tanks and also try and feed power to the pump in the front tank. That will confirm what is going wrong.

Search the site, I know there are plenty of dual tank problems to search from. Just remember that the switch recieves power and sends it either to the front tank or back, not both. Also it switches the sender so the gauge reads the tank thats selected.