1991 F150 did recall, one way valves, still pumps fuel back into other thak.

A check of fuel system parts for your model turns up a "distributor check valve" and a "fuel tank selector valve." The check valve is disk-shaped, with hose fittings coming out of the center of each side. One side of the disk is white and the other side is black. Make sure you note which way it is oriented in the line if you change it.

The fuel tank selector valve is operated by the tank selector switch.

If you do not have any separate check valves in the system, see if your vehicle is subject to a recall. I see on some other sites that there was a problem with the fuel regulator returning excess fuel to the front tank only, causing it to eventually overflow if the front tank is not used from time to time. The check valve is supposed to help with that problem. There is also a recall on the fuel pressure regulator - if it fails, it can damage the check valve in one of the fuel pumps, allowing unwanted fuel transfer. I've included a link to a listing of recalls for your vehicle - do a page search (Ctrl-F or Command-F) for "fuel." In particular, you should look up recall # 93V125000.

http://www.autobytel.com/ford/f-150/1993/car-recalls

Is it possible the fuel hoses are not hooked up right ? If you only changed the rear pump and the lines are correct, its possible the new pump damaged the check valve in the front pump. The valve could have been about to fail before replacing the rear pump.
You may be able to block the line going into the front tank and run the truck from just the rear tank.

it could be the PCM , but I would check the fuel pump relay first. the relay could be sticking to make the fuel pump run all the time. as far as the dying problem you may want to check the idle air by-pass valve to make sure your idle rpm's are sufficient.

Have the same truck and had the exact same problem. Mine spilled out the front tank. Ford did a recall on this problem. They put valves on the lines outside the tanks. Mine had already been done so that was not the problem. The pumps have valves inside for the return lines. I replaced the rear pump, didn't fix it. Replaced the front pump and Voila ... it was fixed. Bad valve in the front pump return line.

Check your fuel selector valve for proper working condition. The internal valve may be stuck.

From what I can find out Ford did not use a fuel transfer valve in 1992. They ran both pumps to a common fuel line and used one way check valves to keep one pump from filling the other tank while keeping the entire fuel system pressurized. Your tank selector switch is actually switching pumps off and on, not a transfer valve. The problem Ford had was the one way valves failing causing one of the tanks to overflow. They have an external one way valve kit to solve this problem, but the valves are about $85.00 each.

check your relay and your fuel filter should be replaced every 30,000 miles

on the left hand frame rail ahead of the front tank there is a valve that controls which tank the truck runs off of it is bad let me know how you make out
p.s. if you dont wantto replace right away just run the tank that over fills down first and monitor when you switch over to the other one

your truck is a 4.9L, make sure you have power to the front tank fuel pump. is the power to the pump is ok and you can hear the pump run for a second or two when you key the vehicle on... replace the fuel tank selector valve

Please Help ME by Remembering to RATE ME Thank you Vrey Much !!!

This vehicle does not use an external fuel tank switching valve. A supply check valve in the fuel pump assembly opens when the outlet pressure from the energized fuel pump exceeds the opposing check valve spring force.


R E C A L L 1991
THE DUAL FUEL TANK SELECTOR VALVE MAY MALFUNCTION AND CAUSE AN OVERFILL CONDITION IN ONE OF THE FUEL TANKS, RESULTING IN AN OVERFLOW OF FUEL PAST THE FILLER CAP.
THE OVERFLOW OF FUEL PAST THE FILLER CAP CAUSES A FUEL LEAKAGE, WHICH CAN RESULT IN A FIRE WHEN EXPOSED TO A SOURCE OF IGNITION.
REPLACE THE DUAL FUEL TANK SELECTOR VALVE.
SYSTEM: FUEL TANK, AUXILIARY.
VANS AND LIGHT TRUCKS WITH DUAL FUEL TANKS PRODUCED IN THE FOLLOWING PERIODS: F150, F250, AND F350 LIGHT TRUCKS BUILT BETWEEN FEBRUARY 28, 1989 AND JULY, 1989; ECONOLINE BUILT BETWEEN FEBRUARY 28, 1989 AND FEBRUARY 11, 1991.
NOTE: FORD HAS AGREED TO RECALL THESE VEHICLES BUT PARTS ARE NOT YET AVAILABLE.PARTS WILL BE AVAILABLE IN DECEMBER 1991. YOU WILL RECEIVE A LETTER FROM FORD ADVISING YOU WHEN TO SCHEDULE AN APPOINTMENT WITH YOUR DEALER TO HAVE THE RECALL WORK PERFORMED. IN THE MEAN TIME, YOU CAN TAKE THE FOLLOWING PRECAUTIONS:FILL EACH TANK TO ONLY 1/3 FULL. IF YOUR VEHICLE LEAKS FUEL OR IF YOU SMELL FUEL, STOP USING THE VEHICLE AND CALL FORD AT (313) 446-4654 AND ADVISE THEM OF YOUR PROBLEM. REFER TO FORD SAFETY RECALL NUMBER 91S39. AN OPERATOR WILL TAKE YOUR NAME AND TELEPHONE NUMBER. A FORD REPRESENTATIVE WILL CALL YOU BACK