2000 F150 would not start. No fuel pressure. Pump would run for one second then stop. Relay and fuse ok. Replaced the pump and shazam good pressure and truck runs great. Just for grins I tested the pump with 12 volt battery charger and it ran fine. What gives?

 

The fp runs for 1-2 seconds when you turn on the key which primes the system and then waits until the engine hits the 400 rpm cranking threshold to start pumping again. It doesn't sound like you had a bad fp.

 

ONELOWF: I agree with you to some extent, however I did spray gas into the intake manifold and it fired up and exceeded 700 RPM. I know that pumps used to be powered off the oil pressure switch and the 2004 and up off a fuel pump driver module. On the 2000 I think the PCM somehow grounds the circuit after the relay drops out. Anyway after droping the gas tank I was not about to put the old pump back in. Thanks for the reply.

 

On Ford fuel injection since the first 'full' injection in 1985 (not throttle body injection), the 2 pipe systems fuel pumps were never powered through any oil pump switch. When the single pipe system came into use, the control system was altered to use a different control and a pressure sensor.
An inital ignition switch to run position started a short timer in the EEC/PCMs that powers the pump relay that passes power to the pump through a crash sensor and independent fused power source..
In cranking, the PIP in the EEC systems and the crank sensor in the PCM system signal the EEC/PCM to restart the pump full time as long as the crank is turning.
The reason the pumps are controlled thru a relay is for safety and other reasons of no direct EEC/PCM high curent controlling..
The crash sensor in series can disable the power to the pump to prevent feeding a fire if the motor does not stop running (or) the ignition switch is still on Run.

 

Bluegrass: Thanks for the info. My son tells me it was his GMC truck that took power off of the oil pressure switch not my old Ford. I was wrong. However, I still can't figure why the pump would not run for longer than a second or two, then would run ok hooked to a battery charger. It is running fine now. I am a little nervous about going on a five hundred mile trip with it without understanding what was going on. We will find out tomorrow if it is ok when I head out to Louisiana. Thanks again.