I have a 1991 f150 that I replaced the original engine at 220k with a Jasper crate motor. The old engine was starting to show alot of signs of wear and after window shopping for a new truck I decided to go the cheaper route. The problem I'm having is the truck will run fine and then just quit. After it sits for awhile it will start and run fine. I have replaced the alternater,battery, icm, distributor, coil, ignition harness, the pcm, both fuel pumps and fuel tanks. After doing all this I surrendered and took it to a local shop with a good rep. and after three times back to the shop they are just as perplexed. Any thoughts would be greatly appreciated.

 

The engine runs perfect, and then just up and quits while your driving? And not throwing any codes? Sounds like a sensor crapping out.

 

Does your year truck still have the TFI module on the distributor?
If so, it sounds like the TFI module is having heat issues. This is a known problem and why Ford moved it to a heat sink on the firewall in later years. Replace the module.

 

That was my thinking. I am just tired of the parts swap. And no I'm not getting any codes.

 

Sorry to throw out a random guess, but it sounds like you are trying to cover all the bases. Do Fords use a crankshaft position sensor? I know GM model vehicles of that era did, and when they went out, the car/truck is deader then a hammer. If such a thing were intermittent, that would cause random stalling. Someone already mentioned a possible dead sensor...I just think this might be a likely culprit.

Good luck!

Mike


FYI...try to find a place that has a real-time ecu monitor. In other words, a computer that can be hooked to your vehicle that displays the actual sensor readings while the engine is running. If you can duplicate the problem while watching the sensors, you should be able to pin-point the issue.