Had a very good example of how this particular coil pack fails from heat over the years. The misfire may be intermittent or only when wet out. Either way this particular coil pack style which is used in the Taurus Windstar and 4.2L F150 all fail the same way. If you have a misfire you are fighting I urge you to take a closer look at the coil pack as shown for these common signs.

 

This should go in the little 4.2L Forum on this site.