zeroptzero

Do you have a shop manual ?, there should be a procedure / flow chart to test the voltage at the connector and the resistance on the coil. If you need the info pm me and I can look it up, otherwise I'd say begin testing those two items.

Billman250

Is it possibvle the threads are damaged, and the spark plug is not going all the way down and seating?

Remove the number 4 coil, disconnect the number 4 injector, and run the engine for a minute without that coil. It there hot air coming up out of the plug hole?