Misfire 2001 Ford Focus ZX3 ZTEC DOHC

2001 Ford Focus ZX-3 DOHC ZTec P0351 Ignition Coil ‘A’ Primary/Secondary Circuit:

While test driving my Focus, it suddenly developed a misfire. I found the wires from the computer to the coil were resting on the hot EGR pipe melting the insulation on one of them causing it to short to ground. I pulled the wires off and zip tied them to keep them off of the hot pipe and I covered the bare spot on the one wire with liquid tape, but the misfire didn’t go away.

My question is: would that signal wire from the computer touching directly to ground with no load in the circuit damage the driver in the computer? In other words, do I need a new computer now?

Thanks

My question is: would that signal wire from the computer touching directly to ground with no load in the circuit damage the driver in the computer?

Since this ignition coil uses ground side drivers for the primary coils, it's *unlikely* that the PCM was damaged by the short to ground.

However, there are variable there. While the wires were bare, did they touch each other? If there happened to be a B+ wire in there (like the B+ feed for the ignition coil), and it touched one of the coil control wires while roasting on the EGR pipe, then that'd smoke a driver in the PCM.

In other words, do I need a new computer now?

There are some quick checks you can do with some inexpensive equipment to determine that. This is the ignition coil connector view for your Focus:



Disconnect the ignition coil and turn the key on. Use an incandescent test light connected to B- and gently touch the middle pin of the connector. It will light brightly.

Then, connect the test light to B+ and gently touch pin #1. Don't get mean with it - just gentle contact. Get someone else to crank the engine and observe the light. It should pulse regularly. Do the same with pin #3.

Do both wires pulse? Then the PCM is controlling both circuits and probably isn't smoked. Does one pulse but not the other? Then we need to keep digging.

The pcm wasn’t damaged because, as you pointed out, the drivers in the pcm are on the ground side of the circuit and the short to ground was upstream from them. The coil did take a beating though. Melted and cracked it. https://ibb.co/s5Y84ZH