Working on the latest mechanical debacle with my ‘08 F-150. It’s a four wheel drive STX with the two valve 4.6L. I need the wiring diagram for where the harness connectors plug into the PCM. Wanting to check continuity of the control wires for the COPs. The truck shakes like a cylinder is misfiring, but only slightly at idle, and a lot between 1200 and 1400 RPM while driving. I can’t feel anything abnormal at 2000 RPM or above. Code says “coil C primary/secondary”.
The coil tests 5.95 ohms from both the power and the control terminal to the end of the spring. All the plugs are new Motorcraft plugs. The connector is good. The power wire shows 12.1 volts with the switch on. I’ve put a test light on the #3 coil control wire & battery positive with the engine running & the test light blinks, but I was thinking the wire could be partially broken or shorted to power somehow.

 

 

Have you actually tried swapping coils?

 

I haven’t. I’ll swap #3 with #2 & reset the check engine light today. Supposed to leave it with a mechanic this week to have the valve cover gaskets replaced, and I’m going to ask him to check for a vacuum leak while he has it.

 

I pulled that new #3 coil to swap with #1, and realized the power prong was bent against the top of the plug. Even though the connector clicked each time, the power prong wasn’t inserting into the power pin. I straightened the prong, but still swapped it with #1. Drove it a couple miles & back. No check engine light now, but the vibration is still there at 1200 rpms, and it still doesn’t idle well in gear. Thanks for reminding me to swap it with another.

 

That new coil that had the bent prong on it was bad. Threw another check engine light this morning & when they read it, same error, except in #1 now. So they made it up, and I replaced it in the parking lot.
I’d been driving it in limp mode for a week, and the exhaust had already started making a clanging sound. That went away when I replaced the coil. Thanks for both y’all’s help.