Okay guys I need some information. I have a 1991 F-150 4x4 w/a 5.8L (351) and EFI. When I bought the truck in 2001 the rear tank was leaking (but it worked), so after one failed attempt at fixing it, I just used the front tank. Well this summer the front tank started leaking. So after a lot of work I got both tanks to stop leaking but when I tried using the rear tank I couldn't get any gas from it. So naturally while I had things already apart and I was in the mood, I checked the fuel pump in the tank by taking it out and hooking directly to the battery and it worked. So after making sure that the front tank worked I got under the truck and with the key on I hooked up a test light to the plug for the rear tank and had my assistant (otherwise known as my wife... ) switch from the front to the rear tank and the results weren't good. At first I got juice but it only lasted a second and then it quit. So now I am still stumped at what is causing the front pump to work and not the rear. Is there a chance that the fuel pump relay under the hood has two different circuits (one for the front and one for the rear), or is there a fuel pressure switch that is telling the relay that the rear tank is already putting out enough pressure and shutting it off??

Someone must have had this problem or knows what is wrong. Please help.

John

 

Likely just a poor/corroded connection, not at all uncommon with these trucks, but usually it shows up in the fuel gauge reading improperly before affecting pump operation.