My seldom used 99 F150 V6 has about 175,000 miles on it. About 18 months ago I replaced the fuel pump($170). No problems. I last drove it about 2 weeks ago and parked it. We have had a lot of rain and the truck stays a little damp on the insides. I tried to start it and it died. I tried to restart it and noticed that the lights on the panel were flashing and the gauges were bouncing back and forth. The Engine turns over fine. With a little gas added to the intake it runs for a second. I checked the intertia switch and the button is down. I replaced the 301 Fuel pump relay, I checked the fuel pump fuses. I finally pulled the bed to access the fuel pump. I used a volt meter on the two left wires and it was 12 volts so I thought fuel pump again. This time I only replaced the pump ($80) portion. The pump is still not coming on. I realized that the two wires that feed the fuel pump are the top left(red) and the bottom Right(Black). With those two I only register @ 7 volts with the key on. Any suggestions? If I am testing the correct wires, I think I may have an electrical issue. I dont recall the instrument panel going nuts the last time I replaced the fuel pump.

 

Do you realize that the pump is only turned on for about 2-3 seconds when the ignition switch is first turned from OFF to RUN and that is the ONLY time that a voltage check of the fuel pump feed is valid until the engine fires?

 

I am pretty sure that I checked it as the key was turned. I will double check that. Voltage or not, the pump is still not kicking on. I left the bed off so that I could monitor that and hear it better. Thanks.

 

Well, confirm that you have it's power and ground at the pump. Then, if its not kicking on, it's the pump or the wiring between the connector and the pump. Either way, it's going to have to come out of the tank.

 

Having someone turn on the key each time, I tested the top left red to the bottom right black and got 7 volts. I believe the top left red and the bottom right black feed the actual pump. Then tried the top left red and grounded to the bed and got 7 Volts. I will check the output from the inertia switch next. If it have 12 volts coming out, I will look for a problem in the wiring between it and the fuel pump harness. If the inertia switch only has 7 coming out, I will look at it. One more question, I am pretty sure that the 99 doesn't have a Fuel Pump Control Module above the spare tire that are known to fail. Is that correct?

 

Yes. The FPDM is later. 04, I think. Someone would have to look it up to be certain.

 

the older trucks have a pressure regulator under the hood that dumps back to the tank. The "after 2004" have the electric pressure regulator module on the rear axle.
----- you should have a shrader valve on the fuel rail under the hood. You can check pressure at that point if you have the pump running. I don't see what would drop the voltage to 7 volts unless you have a corroded power wire, or a bad ground wire.