Why is my rear tank draining my front tank?

Lonesome7.3 · Oct 21, 2010

When we are driving our 96 F250 gasser on the rear tank is sputters and tries to die out. Even with a full tank it runs like it is almost empty. The strange thing is it is sucking fuel from the front tank and over filling. The truck runs fine on the front tank. At first I thought it was the selector valve. I thought it was somehow redirecting fuel into the rear tank due to a malfunction. We even went to the parts store and bought a new one. Well guess what… this truck does not have one. It has a block that all the fuel lines converge into. So I now believe the sending unit in the rear tank is bad. That would explain the sputtering. But how do I explain the removal of fuel from the front tank to the rear?

towcat · Oct 21, 2010

your fuel switching valve has major issues.
change it immediately. gassers tend to go fireball on this whereas diesels just make a huge mess.

Lonesome7.3 · Oct 21, 2010

That is what I was going to do. But this truck does not have a valve. There is a block where the fuel line all meet and that is it.

MUDKICKR · Oct 21, 2010

let me see if i can explain this.
the 92 up f-series gas trucks only have a "tee" type of connection between the two tanks and do not use a selector valve, they have a one way valve in the fuel pump assy. so what happens is when you switch the fuel tank switch from rear to frt the rear fuel pump assy one way valve is supposed to close and not allow fuel to either enter or exit the tank til said fuel pump is turned back on. if the fuel pump is going bad the one way valve might not be closing and letting the frt pump fill the rear tank while running the engine. (pumping fuel into the other tank since valve isnt closed) and also overfill the rear fuel tank til it comes out the filler tube. i hope i explained that so you can understand it.

Lonesome7.3 · Oct 21, 2010

That is a big help. Thanks! So I take it I need a fuel pump? I just want to make sure I understand.

MUDKICKR · Oct 22, 2010

Black dawg · Oct 22, 2010

some of the ford gassers in that era have a round black deal that the fuel lines go through. pressure from whichever fuel pump is turned on move a diaphram inside switching pressure side and return. some only switch the return. Does this truck have a frame mounted pump also?

MUDKICKR · Oct 23, 2010

Black dawg said:
some of the ford gassers in that era have a round black deal that the fuel lines go through. pressure from whichever fuel pump is turned on move a diaphram inside switching pressure side and return. some only switch the return. Does this truck have a frame mounted pump also?

they changed from that system to a completely different system in 1992.

Lonesome7.3 · Oct 24, 2010

For some reason I thought this truck had a frame monunted pump. I was mistaken.

Why is my rear tank draining my front tank?

Lonesome7.3

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