So this morning my dad went out, started his 1991 F150 4X4 RCLB 5.0L E4OD, went to pull out of the shed and it died after 6 feet, won't restart. Got in his Super Duty and came to my place. We went back to his place eventually and I took a look at it. Low fuel pressure, the fuel pumps don't run when you turn on the key. Checked the inertia switch- it was in the run position. Grounded the fuel pump terminal in the OBD1 connector and the pump runs continuously. Hooked up my Snap On scan tool( the cheap OBD1 and OBD2 one) to do a KOEO test and it says that it can not communicate with the ECM. So I was thinking the ECM took a dump, but while I am typing this I am also wondering about the ECM relay. By grounding the OBD1 terminal and the pump running, that should have rule out the inertia switch and the fuel pump relay correct? What should I check next and how? Unfortunately I don't have much time to put in this or to even research this as we are making hay and getting busier than hell on the farm. All constructive help is appreciated,, thank you.

 

Bump anybody? Help please.

 

I would put check fuel pressure on your fuel rail .You should have 35 to 40 psi.

 

WAY PAST THIS TEST. Did you read my post, I said low fuel pressure BECAUSE the pumps don't run except for when I ground the fuel pump terminal of the OBD1 connector. When I do that, they run contiuously and pressure is 37 psi. I wanted to know what to test next as my code reader says there is no communication with the ECM- is it a bad ECM or is it possible the ECM relay is not powering up the ECM and causing this?

 

I suggest you check Fuse Link N. It supplies power to the EEC relay and the computer (PCM) as well as the coil of the Fuel Pump Relay.

Reference this from oldfuelinjection.com:


On the other hand if the Fuel Pump Relay kicks on when you grounded the return that would indicate Fuse Link N is good. Some basic wire tracing should lead you in the right direction.

 

Bad computer.
Just make sure the computer is grounded at the Battery Neg post.

 

According to the schematic he posted you should check fusible link W not fusible link N which only feeds the EEC relay and the PCM. The fuel pump relay coil is fed by fusible link W.

Sounds like the computer is dead, but check for good powers and grounds to your relays etc first. Then maybe pop the computer open and take a look, not uncommon to find a leaking capacitor causing problems.

 

So I got around to checking it further this morning. I have battery voltage on pin 1 at the ECM, I have switched power from the EEC relay at pin 37, and I have good grounds on the 2 pins that should be grounded for the ECM( I don't remember the pin numbers, 16 and 60 I think). So at this point, I think it is a bad ECM. Does anybody agree or disagree with this?Any other tests I should perform?

 

Sounds like a bad PCM to me at this point. If you put a meter on the return side of the Fuel Pump Relay you should see it go low when the key is first turned to the Run position. The ground is supplied by the PCM on Pin 8. If that does not go low for a few seconds, it's definitely a bad computer.

 

Is it possible that your fuel selector switch is bad causing an electronic disconnect? I had a bad switch once and it took a bit to figure it out. I could be way off, just a thought