I went to start my 1999 F-150 the morning after I'd charged the A/C system to find it would only cranked. Checked the fuel pressure and there was none. Checked the fuses and swapped the relays, but everything seemed fine so I decided it must be the fuel pump; despite replacing it only a year prior. I replaced the pump again and the problem persisted. Brought out the test light and found there was no power going to the fuel pump or the inertia switch. Back to the fuse box, I find that the fuel pump relay is receiving is constant power through the fuse and power from the PCM relay when the key is on. However, no power is going out the line to the inertia switch and when I test the direct line to the PCM I can hear the relay switch. Thought maybe the PCM has gone bad, so I pulled it out, but there is no smell of burning plastic or signs of degradation. I would rather not purchase a new PCM if not necessary. I've already made that mistake with the pump. Is there another cause for this issue? I've checked the wires as best as possible thinking there could be wear and tear somewhere, but I was unable to find any. Any help is appreciated.

 

The fuel cutoff switch?

 

He said he checked the Inertia switch power already. That was my first thought.

Reading the system info, I believe the OP is on the right track with the PCM not sending a signal to the pump. We had one on here this fall that came up with this as the conclusion. He swapped out the PCM and everything came back. Time to run that signal and see if that is the actual problem. Since it sends the signal to the pump, it's almost got to be there, or a wire/or ground problem.

 

If it is the PCM it should be throwing a code between the FPM in the PCM and the PCM.

 

I had the same issue. As it turned out the fuse/relay box in the engine bay has a large copper plate that feeds the relays and fuses. This plate may corrode and create an open circuit. The contact from this plate to the relay is at the end and it's the first one to go when the plate corrodes. Good luck.

 

Is the PCM properly powered and booting up? It has to do that successfully in order for everything "downstream" to function. I don't see any evidence that a scan tool was ever used.

BTW, just be aware that, if the PCM must be replaced, PATS will require re-programming. It is not a simple PnP swap.

 

So it's been 24 hours since you posted, any progress?
Did you accidentally disconnect a sensor that is telling the relay not to close? How about a direct jumper across the feed relay to test the pump and confirm the relay is not closing.

 

I didn't have a obd reader when I started and by the time I got my hands on one, I'd already pulled the PCM and disassembled it to see if there were any visible signs of wear. There was not and there was no smell, but any codes stored would have been erased.

My concern is that when I direct power to relay wire that should go out to the inertia switch and on to the pump, there still isn't any pressure and I can't hear the pump come on.

 

Are you saying there's a grounding plate within the fuse box? Why wouldn't the PCM relay go first under this logic sense it's further? Is the diagnosis to disassemble the circuit box? There is power coming in from the fuse and the PCM relay. No power going out to the inertia switch. And the wire directly to the PCM causes an audible switch click when grounded.

 

Didn't have a reader until after I had disconnected and disassembled the PCM. No signs of wear or burnt odor, which makes me even more hesitant to seek out a replacement. When I did get a reader on it, it was able to communicate with the PCM, but all codes stored were lost. I'm concerned there is some other failure down the line.