I've heard about this problem before from reading the forums.

So here's what my truck did.

I have a dual tank set-up in my 93 f150. I replaced the front tank a couple months ago with a used tank/fuel pump. The sending unit doesn't work, but the fuel pump does and I was happy to have two tanks with working pumps.

When I fill up, I fill both tanks. This last time I drove on the rear tank till it was down to about 1/4. Then I switched to the front tank which is alway son E(mpty) because the sending unit doesn't work. But while I was going down the highway, it started running out of gas as I was talking on the phone with my girlfriend. I hit the tank selector switch on the dash and switched back to the rear tank, and the gauge went up to 1/2 tank, even though I'm sure it wasn't more than 1/4 full when I last used it.

So is that my fuel tank selector valve going bad and pumping the returning fuel to the rear tank instead of the front?

I picked up a new part this weekend, but I looked under there i can't even find the damn thing.

 

its right under the drivers door on the frame rail just trace your lines and you should spot it.

 

Man, this is a hot topic lately.

Yeah, the valve is the cylindrical object on the side of the frame rail with six fuel lines going to it.

 

Finally done mine this weekend. it was a PITA. Had to figure out how to plug the lines to prevent gas from draining out of the tanks. Hopefully it's fixed and I won't have to do thsi again......

 

A 1993 does not have a selector valve.
Only the selector switch on the dash.
You have a bad check valve or shuttle valve in your rear Fuel Delivery Module (assembly).

Fuel Delivery Module (assembly) or FDM.


Your fuel system.


Your fuel wiring.

/

 

bogus... that's not cheap

you could always do what I do on my 88...
run the front tank empty
run the rear tank empty
run the front tank empty again
fill both tanks

because YES, I AM TOO CHEAP TO BUY THE PART!

 

So the fuel from the front tank is being returned to the rear tank because the rear tank module's check valve isn't functioning properly?

 

Yes one of the valves in the FDM is bad in the rear tank, either the hi pressure check valve or the shuttle valve.

 

I just bought a 1994 Ford F-150 for my daughter. It is pumping fuel to both tanks depending on which one it is on and over flowing both tanks. What part do you suggest I change?

 

To me, it sounds like both FDMs have bad check valves.

 

I have a 94 f150. I have the same issue with filling up front tank, fuel go into rear tank. I looked for a selector valve and didn't see one this is all i saw where tanks lines come together. So do i need to change entire fuel pump assembly to fix problem?

 

According to others here, Ford stopped using the Dual Function Reservoir sometime in 1990. I assume you have already read the whole thread and already know the answer to your question which is “yes”.

 

Yep, I kinda thought so, but now I know. Thanks

 

So my front front tank is pumping gas into back tank only. Back tank is not pumping into front. Which FDM is bad ?

 

The rear FDM has a bad valve. The tank that gets filled is the one with the bad valve. Could be the check valve (supply side) or shuttle valve (return side) that's why the best practice is to replace the entire FDM.


courtesy of Subford