i have a 93 F250 everything is brand new including the fuel tanks and pump currently when fill up both tanks and run down the fuel in the front tank i will switch to the rear tank and while the truck runs fine i noticed my tank level was dropping fast like 10 gals in 15 mins. So i flipped back to the front tank and noticed that was rather full. I was told it was because the fuel pump is for a single tank and not for dual tank set up. Can anyone shed some light on this

 

Do you have one of these on your frame? It was used with the two-pump system -one in the tank (one in each tank), one on the frame, with this thing before the second pump mounted on the frame. This thing in the picture is called a dual function reservoir and is what switches from one tank to the other based on which tank's fuel pump is switched on. They're notorious for that problem you're describing.

If you do NOT have that system, and just have the single pump in each tank, then there's a shuttle valve built into each in-tank pump assembly, and that can be a problem...

 

that year should be only two pumps one in each tank

 

You should have a fuel pump in each tank, They are actually called FDM (fuel delivery module) with the supply and a return, when switching between tanks the pump that is pressurized opens the shuttle valve selector which lets the fuel return to the proper tank, The shuttle valve is spring loaded so the tank that is not energized will seal off the return to the tank that is not on. Make sure you have the right fuel modules in the tanks, and that they are working, if the shuttle valve sticks than fuel returning from the engine can go into the wrong tank. Quick test is to disconnect the return line at the engine, put a hose on the return fitting on the fuel rail and put the hose into a bucket blow into the return, have a friend stick his ear to the opened gas cap. Switch tanks and blow again you should only have air going into the tanks that are selected.

 

unfortunately i did not do the work on the fuel tanks the prior owner did but i just spoke with him and he said he forgot to give me the FDM for the front tank, So i said to him you told me that you replaced the pump etc...blah blah blah he said yeah i did replace it but it was replaced with a pump for a single tank truck and duels and that why i am having the issue. so he is giving me the proper FDM today hopefully this will solve the issue.

thanks for the responses. this truck is a real gem just so many small issues but day by day dollar by dollar she will be back to new status soon (i Hope)