Ford Repair: Fuel Pump - 96 F150 4x4 with 300 6 Cylinder, battery voltage, fuel pump

Question
I just purchased this vehicle. The problem is that when the tank selector is on the rear tank, the truck just sputters and dies when I try to start it. When I switch the selector to the front tank it starts up fine. Then, while driving, I can switch the selector back to the rear tank and the truck will still run fine. It only prevents it from starting. Both tanks have gas in them.

What do you think this is? Does the fuel pump sometimes get to the point that it is going out and won't start the vehicle but will allow it to run?

Answer
It does sound like a weak/failing fuel pump.  I would say that since battery voltage is higher when the engine is running, your rear fuel pump is able to move fuel.  However, when you start from that tank, the starter is already drawing most of the battery's power and the pump can't build enough pressure.   You my be able to test this "theory" by starting from the rear tank while a battery charger is hooked up and set to high- that would boost battery voltage and you could see if the truck would start from the rear tank.  Good luck,
Jason