92 F150 fuel related problem?

[CDX825]

I have a 1992 F150 5.8 I'm having a serious issue with. The truck once it been run for awhile starts acting strange. If I turn the key on with engine off the fuel pump will stay running. If you start the truck like this it has no power and will barely get out of its own way. If I cycle the key a few times it will shut off like normal and I can start the truck and it runs fine. Doesn't matter if I run the front tank or rear tank.

Also when you do start it up and its acting funny the check engine light will come on. It has got to the point of where its starting to do it going down the road and that is a real problem. If I stop and pull over and shut the truck off and cycle the key till the pump turns off I can restart the truck and continue on my way.

I have tried replacing the fuel filter and fuel pressure regulator thinking it was one or the other. Took fuel pressure readings and they look normal. Tried pulling the codes with multiple code readers and didn't have any luck. I'm at a loss as to what it could be.

 

[The_Jeff]

I suppose the first best test would be of fuel pressure while it's running.

IDK how fords prime the pump, but that sounds off, too. Relay?

 

[Kik]

If it's doing it on both tanks, then I doubt it's your pumps, unless you have a high pressure pump on your frame also, but I don't think you do. The pumps stay running and you're cycling the keys back and forth to stop it, I'm going to say, it's either the connection on your PCM, maybe some corroded or shorted pins, or your PCM is heading south, probably bad capacitors, if you want some expert advice, Go over to ford-forums.com and go into the older truck section, I have a 95 F250 with the 5.8 and these guys are a wealth of knowledge.

 

[exranger06]

Sounds like a bad computer to me. When you turn the ignition on, the fuel pump should only run for a few seconds and turn off. The computer is what controls this. The fuel pump relay is controlled by the computer. If the fuel pump continues to run, it's because the computer is telling it to keep running. It could also be a sticking relay, but since it also happens when the truck runs badly, I think there's something wrong with the computer. What do you mean when you say you didn't have luck pulling codes? No codes came up?

 

[CDX825]

Originally Posted By: exranger06
Sounds like a bad computer to me. When you turn the ignition on, the fuel pump should only run for a few seconds and turn off. The computer is what controls this. The fuel pump relay is controlled by the computer. If the fuel pump continues to run, it's because the computer is telling it to keep running. It could also be a sticking relay, but since it also happens when the truck runs badly, I think there's something wrong with the computer. What do you mean when you say you didn't have luck pulling codes? No codes came up?


Ive tried a couple different code readers and they dont ever come up with anything useful.

 

[exranger06]

What do you mean by anything useful? Do you get just get the code 111, which indicates everything is fine, or does the code reader just not communicate with the computer?

 

[Silverado12]

It's been a long time since I've worked on one, but fuel pressure regulator problems were common on those.

 

[punisher]

Originally Posted By: exranger06
What do you mean by anything useful? Do you get just get the code 111, which indicates everything is fine, or does the code reader just not communicate with the computer?


Stole my question.

Sometimes you have oddball situations where the manual is no help. I am about 50/50 in actually fixing vehicles with a PCM replacement. Three misses that stick in my mind were a shorted PFE sensor that killed the 5V rail, a bad 60 pin connector at the PCM, and a bad PCM ground.

Before you condemn a PCM (which is still near the top of the list as a possible cause) ck the connector, get a pinout diagram and ck the grounds, or check the ground to chassis connector the PCM uses and verify they are tight/not corroded. Problems like this where you might have a bad PCM, unreliable power supply/ground, or at least unreliable diagnostic information from the PCM, just makes you nuts sometimes.