Mechanics

F150 FUEL PRESSURE PROBLEM

1996 Ford F-150

Engine Mechanical problem
1996 Ford F150 V8 Two Wheel Drive Automatic 212000 miles

I'm having a problem with my truck maintaining fuel pressure. It has 32psi at the rail when I start it, but it soon drops, causing the truck to sputter when you try to accellerate. I have taken the pressure regulator off and attached a hand vacuum pump and it holds steady at 40psi. I have good vacuum on the line that plugs on to the Regulator with no gas smell. I have also changed the rear tank pump and I am getting no pressure when I switch to the rear. I can hear it run, so I am a little confused. I have replaced the plugs, cap, rotor, wires, fuel filter and TPS sensor. I am at a loss on this drop in fuel pressure. Any help will be appreciated.
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Kaduh
February 13, 2010.




Probably by-passing the pressure into the front tank. Those trucks had issues with erear tank fillin gup thefront tank. There was a inline check valve that was used for awhile, but I didnt hav eany luck finding one last time I tried. Try switching to the front tank, checking the fuel level. Then run the rear tank and see if it is filling it up. If it is equipped with a fuel switching valve instead of just pumps, the switching valve is probably bad

Tiny
Jack42
Feb 13, 2010.
I got under the truck yesterday because I kept reading about a fuel selector switch and wanted to see if there was one on mine that may be bad. The only thing I can find is an aluminum manifold where both the front and rear fuel supply lines tie in to that has one main supply line going forward to the engine from that point. I understand what you are saying, because I had to replace the front pump seven years ago because of the same issue you described, but this time I am stumped.

Tiny
Kaduh
Feb 14, 2010.
If you had to replace your front pump for that issue then you dont have a selector valve, the check valves in the pump do the same thing. You neeed to be sure the fuel pump is still getting power when it loses pressure. Did thefuel pump for that come as an entire tank unit or just a pump that you replcae on the sending unit? Ifit was just the pump, was there anything between the pump and the sender other than just a piece of high pressure hose? If so it may have a bad pulse dampener in there that is allowing the fuel pressure to bypass right back into the tank. They wil lmake pressure against a closed system, but when you start bleeding off pressure (running engine) they lose pressure. If you suspect that pressure is being lost outside tank, remove fuel pressure line at junction and install pressure gauge there to see if it making it to junction, but being lost in it
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Tiny
Jack42
Feb 14, 2010.
I believe it's still getting power because I can hear it, and the engine stays running. It just wants to stall when you try to give it gas. I think they just replaced the pump itself, which just slides off of the sending unit with a solid aluminum pipes that go into it. The only high pressure flex line is on the outside of the tank that goes to the junction manifold. I guess I need to go ahead and replace the front pump and see if that helps. I can order one online for $50, so it's not that bad, it's just a pain to drop the tank!

Tiny
Kaduh
Feb 14, 2010.
Its easier on some trucks to unbolt the bed and get a friend to help you lift it and slide it back, then the top of the tank is right there.I would double check with a pressure gauge before I replaced anything, so you dont waste time /money in the wrong direction

Tiny
Jack42
Feb 14, 2010.

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