i have a 2003 f350 5.4 with a cylinder 4 miss fire injector is working and so is the coil, cylinder compression check on 125 psi but on the spark plug it self it has an aluminum shell with bigger threads since somebody rethreaded with the wrong thread could that be causing the missfire?

 

Has this just suddenly started happening?

 

nope it was bought that way

 

How do you know the coil is good. I've gone though a bunch of them. Could be the plug but the threads have no effect. If the job was done right the plug that was ejected should have been repaired using the Tap System. Using the kit you bore out the old threads tap the head, insert and lock into place a special steel sleeve that leave the same threads as the stock plug. I had a V10 the ejected 8 plugs.