Ford F250 Dual Tank Problem

I'm working on a friend's '95 Ford F250. The front gas tank ran out of gas a little while after being filled. All of the fuel is now in the rear tank - which hasn't been used for over five years.

[karljay]

I just had that happen to me and it was because of the selector valve. Opened it up and there were two o rings out of place, one was down in the bottom of the plastic filter part. The rear tank didn't even have a pump in it and wasn't used for 20 years.
It's the fuel selector valve and seems to be because the glued in valves at the bottom in the little screw cap filter part fail. These are glued in and can't be removed easily. Getting a simple valve as a replacement would be the better choice, a solenoid operated one would be a good choice.

[frankmadonia]

how do you fix this? mine’s doing the same thing!

[altonlynch]

I own 2 ford F150's and I have never seen anything like that. I'm putting new fuel pump in front tank right now. It's been acting up lately, then the other day I got in it and the fuel pump was super loud, so I figure it's about to go out. Time to replace it.

[omgbbqcia]

whichever tank is overflowing has a bad return check valve in the sending unit.

each tank's sending unit should have a check valve inside the tank on the return line. when the fuel pump is running, a check valve in that sending unit opens to allow fuel to return into the same tank. when the fuel pump is not running, the check valve closes so gas cannot flow through the return line. if you are running the rear tank but gas is returning to the front tank, then the check valve in the front tank's sending unit is bad and not blocking the return line.

you also need to check when you buy a new sending unit as some sending units dont have the check valve which wont work for a dual tank setup.

[Highspeedoffset]

How could a failed sending unint cause that? Failed selector valve, Yeah sure.