My dad has an 05 4.2L that started missing after hitting a pot hole. 60k mi. I believe. He had it scanned and they found cyl. #3 misfire. Today he replaced all the plugs with Autolite Platinums because a few months ago one of the plugs literally fell apart causing it to miss. It still misses. He replaced the plug wires. It still misses. He replaced the coil pack. It still misses.

Ideas? Injector?

 

Compression check and/or borescope. When the plug came apart it may have damaged the piston or a valve. Shouldn't be using Autolites, the engine really prefers Motorcraft.

If you want to test the injector theory, just swap it with one of the others.

 

He figured it out, had #5 & #6 plug wires switched. Yea, I'm a fan of Denso / NGK Iridiums or like you said the Motorcraft plats, but I didn't pay for em.

 

Only use Motorcraft in this engine!

Please.

 

Iridiums work well too.