Yesterday I was driving in town when the engine shut off. Thankfully, I did get it to start after 2-3 attempts at turning the ignition.

This completely baffles me because there was no coughing, grinding, no shudders, nothing. The engine simply shut off like it normally would, but the truck was in gear and the key was still turned forward. After I got the engine started, the rpms kept dropping every couple of seconds like the engine wanted to stop, but again there was no noise to indicate a mechanical problem.

After I parked it a second time and let it rest for a couple minutes, the engine started and ran normally. I had the battery checked at a Walmart and it was fine, which means I don't think it could be an alternator problem.

Something peculiar did occur though on my drive back. The "check engine" light would come on and off in irregular patterns. It would turn off for a minute, then turn back on for a few minutes, would turn off for 5, come back on again for 1, turn off, on, etc...

Additionally, all the lights, heater, air-con, radio, and the starter still work as normal, so this problem seems to be associated just with the engine and the electronics that make it work.

Ideas on what the problem might be? I assume that if it's electrical, it's pretty common to have a problem where the engine just shuts off like normal, but when driving. It's 1991 F-150 with a 5.0L V8. I replaced the spark plug wires this fall, so distributer cap? coils? It's got 156,200 on the odometer and nearly everything on the truck is the original part from when it was new 24 years ago.

I'll be taking it to the mechanic for sure, but I'd like to get an idea (or a few) of what could be wrong.

Thanks!

--James

 

Quite often the coil or even more commonly the PIP (sensor inside the distributor) will work, not work and work again intermittently when they are starting to die.
A poor connection or a bad ground can also cause those kinds of problems.
If your check engine light came on, the computer will probably have stored a code- Read "just call me sean" 's posting at the top of the 87-96 section on how to check obd1 codes.
Finding a code will get you looking in the right direction usually.

 

I have a 91 5.8 and fought through an intermittent ignition cutting out issue.
Ended up being the ignition module on the distributor. I would vote either module or PIP in the distributor.