I bought a 2001 f250 about 2 months ago. 3 weeks after I bought it, I can tell it was having a missfire problem. So off to the store for some nice double platinum plugs. I checked the gaps anyway before installing them, and swapped out all 8 on the 5.4. This took care of the problem for about 10 days whenI noticed it doing it again. Now after 2 more weeks its worse, not bad at an idle, rough in the midrange, and smooths out if you bury the peddle. Now I'm looking to test the coils, but have found no info on how to or what readings I should get. There has never been a check engine light andI've run dry gas and injector cleaner through the system already in hopes it was something cheap and simple.

 

Guess theres no true coil test unless you have the equipment to load test one, multimeters I hear can be ineffective. My problem turned out to be coil5 failure. So 275 bucks and a half hour at the dealership and I'm roarin again. Next time i'll pay 300 bucks on ebay for new motorcraft coils and do all 8 of em!