LSC ignition problem...HELP !!!!

[kentowski]

1986 LSC, 5.0 EFI. awhile back I noticed a "miss" when I would use the power window, cold mornings only. Thought a bad/shorted motor maybe.The other morning (cold) while driving, engine warmed up, turned on the defroster and the engine started missing badly, parked it, that afternoon drove it, no problem. Next morning same thing, now it just does it all the time, not driving it. Changed the coil, didn't have to, changed the module, didn't have to, checked every fuseable link, all ten thousand of them !! all ignition components look fine. Any ideas ? Can the O2 sensors or other sensors cause this ?

[cougarman]

Pull the plug on the alternator, start the car an see if the problem is gone, if gone, turn off the car and reconnect the alternator to see if it comes back .May be caused by a leaking diode in the alternator. . It's a long shot but doesn't cost anything to try. If that's the problem, replace the alternator.

[kentowski]

Thanks for the suggestion. Alt puts out 14.4V at fast idle, 13.6 at idle, I dont think it's the problem. I've replaced the stator assy, coil, checked all the tests for the ignition mod, new rotor and cap, all plugs and wires good. After doing the stator I let it warm up good, set the timing and test drove it - ran like a charm, thought it was finally ok. Got in it this morning (45 o/s temp) it did it again, with no acc's on. Parked it and I'm looking for a bigger hammer !!!!

[cougarman]

My suggestion has nothing to do with the output of the alternator. It has to do with a slight diode leakage backfeeding and setting up a false command type signal to the processor and other electronics. Testing the alt will show 14.4 when charging. We tested a car for 100 plus hours trying to solve a problem similar to yours. It came down to the alternator, even though it checked out o/k.

I know my suggestion doesn't make any sense, But I've seen it happen.
Try it , It only costs you a little bit of time and if your lucky may solve your problem.



I had one more Thought after posting this,,, again out of the normal,,,
Make sure the starter solenoid on the inner fender is a Ford original, not aftermarket..Ford ones have I beleive a diode inside to also prevent a feedback to the processor.