93 F150 Fuel Always Returns to Rear Tank
 

When the tank selector is in rear, fuel returns to the rear tank as expected. When the front tank is selected, it slowly fills up the rear tank but may be also returning to the front tank. My question is that since I don't see a valve under the truck, the in tank fuel pump must have a valve in it that selects the return meaning that the rear tank valve is stuck open. Correct? Is there a way to repair this or is it a fuel pump replacement project?

on this page see the -(read first post)??--it's on there!!! a pretty common problem -can't remember what it was but you will see it- glad to help :)

That covers F150's that have the selector valve on the frame rail. The later F150's don't have this valve.

*Bump* anyone?

Yes you have a bad check valve or shuttle valve inside your rear FDM (Fuel Delivery Module) that is inside your rear fuel tank. The pump is also inside the FDM.

EDIT:
On a 1993 you need to check the FPR (Fuel Pressure Regulator) also as they had a lot of bad ones that year and the FPR will take out these valves.

There is a TSB for one way check valves to be installed on your tanks fuel pump(s). I can't remember the nember or what years it covers.

Thanks guys. Sounds like I need to check on the check valves and FPR, (I have the gage but haven't done it on this engine yet). I suppose that one way to check if the problem is fuel returning to the tank though the fuel pump is to temporarily block the line?

You have two valves in the FDM. One is the hi pressure check valve that prevents gas from entering the tank from the other fuel pump and hold the fuel pressure after you turn off the key.
The other valve is the shuttle valve and it prevents gas from entering the tank from the fuel pressure regulator when the other fuel pump is running.
The extra hi pressure check valve out side the tank will only work if the hi pressure check valve is bad but will do nothing for you if the shuttle valve is bad.

The FDM.
http://i54.photobucket.com/albums/g9...yAssembly2.gif

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Ah right! I can compare the fuel pressure bleed off between the two tanks to see if the check is bad. If that is OK, then it's the shuttle valve by default. From the pictures on autozone.com, it looks like the fuel pump assy must contain everything including the shuttle valve, so it must not be a separate item. As far as repairs go, this 150.00 won't be the most expensive one recently!

Not sure how you can do that as both the pressure and return line are "T" together and go to each tank.

http://i54.photobucket.com/albums/g9...FuelSystem.jpg

Yes but not all of the ones autozone sells are good ones. Some are even missing the shuttle valve altogether. I guess they would work OK if you only had one tank.

Example of one brand that autozone sells.

https://i54.photobucket.com/albums/g...rtexE2059M.gif

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as noted before --subford you the man!!!-diagrams--love them!!!!if they can't finger them out ?? they need help!!! love ya buddy!!!

@subford, forgot about the fact that you need the pump running. I think at this point I'll just replace the FDM and make sure it's a good brand, complete as it was originally manufactured. Thanks for the help, all.

Not sure what I forgot about.
You said you can compare the fuel pressure bleed off between the two tanks and you can not do that with them "T"ed together.

With the lines "T"ed when you shut off the rear pump and the pressure holds you have a bad shuttle valve and if not you have a bad check valve.
And you can only do this if the FDM is 100% OK in the front tank.

No, what I forgot about. :) Fast typing, bad proofreading.