cptnamr7

I recently acquired this little beauty for pretty much nothing because it wouldn't start. The problem is, it still won't start. I've replaced the fuel pump, but nothing coming out of the hose. When I turn the key on it has 12V at the gray wire at the pump for a few seconds, then goes to 0V. Seems like what it's supposed to do. But then nothing. won't start. I replaced the relay under the hood with no impact either. Not sure if there's another smaller relay somewhere though.

Few questions in diagnosing this further:

1. Can I simply apply a full 12V to the fuel pump without damaging it? Seems like from what I've read it backs off to 5V once it starts, so not sure how to test to make sure the issue isn't the pump itself.

2. Can the oil pressure switch have anything to do with this? From what I've read on the subject it sounds like these were equipped with a safety to kill the fuel pump in the event of loss of oil pressure. The truck ran briefly and the gauge responded at that point. But parked it and it wouldn't start again. Previous owner had the same issue- parked it then wouldn't fire. How can I test the oil pressure switch?

What else can I test to start narrowing down the issue? I'd guess the 12V initial jump is to charge the system with fuel, so if I drain the hose once and then turn the key on again it should fill if the pump is operating?

Any advice on this is greatly appreciated. I need the truck to move in two weeks and can't kill the entire time getting it running. At the moment I don't have much of a means of getting it to a service station either.

Allan In NE

Check the ground at the frame there where the body loom plugs into the fuel pump wiring. Have someone cycle the ignition switch; you should be able to hear the pump run.


Allan

cptnamr7

Pretty sure it's not turning on at all. I had the fuel line disconnected and nothing pumped out. I assume even the quick charge to 12V would get something thru?

Going to try shorting it directly to the battery tomorrow as well as check the grounds. They're spotty at best anyway. If nothing else, I broke all the bed bolts loose today so I can pull the whole thing and have access.

Any idea how to short out the oil pressure switch to bypass it? Or can that be involved since presumably it hasn't entered into the equation when only the key is turned and I've established that at that point the fuel pump isn't kicking in?

Allan In NE

The oil switch behind the distributor is a redundant circuit....that is to say, you really don't need it because the relay still feeds the pump.

However, what you can do is unplug the switch and then feed 12v to the grey wire at that point.

Is the fuel pump fuse good?

Allan

cptnamr7

thanks for all the help. Found that shorting the pump straight to the battery didn't fire, so that helped narrow it down. Found a loose connection/short in the ground wire where it comes out of the top of the pump. Decided to say screw it and replace the entire assembly rather than risk something else going bad again since that's such a giant pain to get to. She's purring now, but I still don't trust her enough to move her. Going to keep starting her every day for the next week before I'll have any confidence this is fixed now.

Allan In NE

Glad you got 'er repaired.

They have two modes: running and dead. If yours is running, slam the hood and forget it.

Allan