I have a 95 F150 with the 351W, I am getting a bad misfire when the engine is at operating temp and only at idle. I replaced plugs wires distributor cap and rotor. That didn’t fix the issue with the misfire. I then moved on to the fuel system, I did a pressure test on the fuel rail and got 29 psi while running, with no loss of pressure with the engine off. I replaced the front tank and fuel pump. Now that the new tank and pump is in it won’t start or run. But it will start and run on the rear tank with the old pump. I have checked and double checked the wiring, pump (to make sure it is a working pump) and all of the grounds, the new pump is loosing voltage, it starts with 12v immediately after the ignition is turned on but will drop to 6.5v after about a second. I tested the fuel selector switch and found that 1 of the terminals for the front tank was bad. replaced the fuel selector switch and checked what I could see of the wiring for that. Checked all of the relays by switching them around and with a multi meter (all of them are working). I have even checked to make sure the inertia switch wasn’t tripped. I’m now stuck trying to figure this out.

 

You did not tell us what the pressure is with the new pump. I am betting on 0. New pumps being bad is not an unusual occurrence. Lots of junk parts out there.

 

I haven’t been able to test the pressure of the new pump yet. I plan to do that today

 

just did the pressure test. It is 0 psi. And the rear is at 27psi while running. thank you for saying that, I was so caught up in all of the what if’s that I didn’t even think to do that simple test.

 

Filter changed?

You know about the 1-2 second prime that happens at Key On-but not start?

The ECU won't give the pumps power unless it sees distributor turning.

Testing a pump in place can be done with a drill battery & some jumper wires.

Just don't run for long

What did the sock look like?

 

I changed the filter about 3 weeks ago. The sock was discolored but not clogged. I put a new sending unit and pump in. when I did the pressure test I got it to start using the rear pump and let it run for a minute or two before I switched it to the front. The pressure went from 29psi to 0. And I couldn’t hear the pump running anymore. It’s looking like it is a defective pump.

 

27 on the other pump is not enough, either. Should be 40-45.

 

I know, I am trying to fix it on a budget and do the rear pump later.

 

Well, if it were mine, I'd put a meter on the incoming harness plug & see if I get acceptable voltage at KOEO prime.

If yes, I'd put my drill bat on the harness pins that I know go to pump motor & verify it doesn't run before dropping the tank again..

Did your replacement pump require harness/plug splicing to match existing?

 

Yes it required to splice the harness. The voltage to the pump KOEO is 12v for 1-2 seconds then Drops to 6.7v. It gets 12v while cranking. But I will put jumpers to the harness to see if the pump will turn on.

 

If it starts and runs, the fuel pressure is most likely okay
Replace the caps in your processor is what I'd do next

 

Not to be a ____ but did you not read the whole thread?

From post 1
Post 4

 

Judging from posts over the years, the most common failures on new module installs are with the spliced in connectors.