Hey new guy here,

I have read on this site until my eyes are sore on this topic and am now going in circles so I joined up and am at the forum's mercy. I have a 2000 F-150 5.4 4x4 (135k miles) with an all too common misfire problem. Here is the time line of events:

*noticed slight misfire, went to autozone had a scan, replaced bad COP and plug (motorcraft) for #7 cylinder. truck ran great for 2 weeks. misfire returns.

*back to autozone, three new cylinders showing up as misfire, replaced COP and plugs as needed. No issues for 2 months. misfire returns.

*heck with autozone I decided, ordered 8 new coilpacks and 8 new plugs. replaced and truck ran great for 3 months this time. misfire returns with a vengance! (current day)

*back to autozone, now a different code is showing up along with the previous "ignition coil malfunction." the new code is a "357" or PCM or ingnition circuit control module failure.

during this period I also replaced the alternator, ran plenty of injector cleaner, and will replace the fuel filter tomorrow AM. also I should note that there was never any water or oil in the spark plug cavities.

Is there a reliable way for a garage to test my PCM?
Could it be that the control module is damaging my COP's?
I'm sure I left something out, but that's a good start.

Thank you to anyone who is willing to entertain this well worn subject.

 

It could be the control module, or it could be a short somehwere in the wiring. I had a mercedes once that was eating coils at $120 each. Turns out the wiring harness was shorting frying the coils. Don't get too worried though, the harness was a known issue for that engine. Just suggesting you check out the engine bay wiring, one wire worn though grounding could do this.

 

Thanks Big Greenie!!

I'm willing to try anything at this point.
I'll get out my voltmeter and flashlight and start looking, worn wires had not crossed my mind but I agree, they could contribute.

Thanks again!!

 

I doubt that any of your original COPs were faulty.
Since you have this history, it's time a tech with a good scanner (not a reader) looks at the program Pids in depth, for issues.
He must know what he is looking at or you won't get any worthwhile value out of the effort.
Some background on the operation of the coils:
The PCM logic arrives at the proper time to fire each coil in time by driving a solid state switch that applies a ground to the coils a short time ahead of when the cylinder needs to be sparked.
When the correct time arrives, the ground is opened, "then the spark is generated" at the plug gap. This is how long dwell time or "coil saturation" is obtained assuring good spark at all times even under very lean fuel conditions..
All the coils have common 14 volts standing on them waiting for the PCM to apply and open ground in the fire order rotation.
Check the big connector for being seated tight on the rear of the PCM.
Your issue seems to be with more than one cylinder.
Hard faults with cylinders normally set code P0301/ to 8.
Point is it's time to go beyond the level you are working at, to find the problem.
Good luck.

 

Thank you bluegrass7.
I agree and have already made an appointment with the supposed local "ford guru" He seemed to have similar thoughts as you have over the phone. He also claimed he can test the PCM. I will make sure I post here to share the resolution if he is able to find it.

Thanks again for your advice!!