Misfire - Cylinder #6, nope now 4
 

2004 Endeavor

Service Engine soon light comes on, engine skipping, check code, it's cylinder #6. Check spark on 6, looked okay. Check spark on #4 and it seems okay too. Recheck #6 and notice it's arcing out through the seam in the middle. Replace coil, $150 at part store.

Drive a mile, stop engine, restart engine, Service engine soon light comes on. Back to garage. Misfire cylinder #4.

Does this make sense to anybody?

A couple of questions, what could cause the cylinders to misfire, or cause the coils to go bad.

And if the coils need to be replaced would cheaper coils be acceptable they're $40 online.

I'll look around here to see if anything comes up during a search.

Thanks