My 1994 F150 runs perfectly, except when it doesn't. The six-cylinder engine has less than 100,000 miles on it and hums along... until it starts to falter as if it is not getting fuel. It eventually dies. But after an hour or so it often will restart and again run beautifully---for weeks at a time! Switching over to a reserve gas tank has helped, but sometimes it makes no difference. It happens when it has run for, say, a hundred miles and is warm and when it has run three miles. It has become a chronic problem. Someone suggested the other day that it might not be a fuel problem as such, but a distributor problem, something called a 'PIP." All I know is that unless I can figure it out and again have a reliable vehicle, I will have to get rid of it. What say ye?

 

Tsounds like a fuel issue to me. Did you check the inside of your fuel tanks, fuel pump or fuel filters? You could have something like a piece of rust splashing around that occasionally blocks the line. After sitting it may just settle out.

 

Fuel pumps, tanks and filter have been checked, pronounced fine...

 

Could be the ignition control module. I've had similar problems you describe, the ICM would get hot and the truck would die. After cooling down it would start up and run fine.
Replaced ICM and no more problems.

 

Except that it has done it when the engine was barely warm--though most of the time it doesn't. It is the inconsistency of the failures that has my mechanic stumped, the unpredictability. There seems to be the beginning of a pattern and then it it dies for no reason or doesn't die when you might expect it to, again, for no reason. Shouldn't a simple faulty engine component be more consistent than that?

 

Sounding like either the PIP module inside the distributor, or the TFI module given the erratic nature. There are resistance checks for these, so to avoid just shotgunning parts at a problem - my Chiltons manual listed the specs but I no longer have it.

 

That sounds promising, particularly if a part can be tested before replacing...

 

If the part was permanently dead OR you caught the part when the truck wouldn't start it could be tested. But if the truck is running normally and you try to test a part, it will likely test good. Atleast that is how I perceived testing electrical parts. Maybe ask your mechanic on that.

 

Good point. Thanks...

 

Yeah, chasing electrical gremlins is hard enough, even before the little buzzards go playing hide-and-seek with being intermittent. Just hate replacing parts on a leap-of-faith rather than definitive knowledge, always that chance of introducing yet another problem with a bad part out of the box, but sometimes you just do what you gotta do.

Had a similar experience with running fine then randomly dropping out. The PIP was just out of its spec'd range, replacing it solved the problem. Whether that was a good diagnosis or just luck, eh, dunno. The values 0.8-0.9 ohms comes to mind, so if correct, it will take a good multimeter - not the $12.95 checkout line cheapie.

Suggest if changing the PIP is decided, consider getting a reman distributor complete with the new PIP already installed. Changing the PIP requires getting the drive gear off the shaft, which is a real challenge given the tight fit and the varnish that has built up. Oh, from personal experience, remembering to remove the roll pin in the gear is another opportunity to excel.