Hi: I've got a '99 F-150 Lariat 5.4 L 4x4 auto with about 57000 miles on it. A month or so ago it started to run and idle roughly, especially during light acceleration. The problem was fairly intermittent at first. I tried better gas and injector cleaner, and replaced the air filter. I bought the truck used with a K&N filter, noticed that the gasket was bad, and decided to just put a Fram filter in instead. No improvement. At some point, the check engine light had come on, so I took it to a shop. They said it was missing on the #4 cylinder. During the course of trouble shooting it, they put it all back together and took it on a test drive. Wouldn'tcha know, it ran just fine. They charged me for one hour of Dx and said to bring it back if it acted up again.
Anyway, it started running poorly within a day or two, and gradually went from intermittent trouble to running badly almost all the time. Based upon what I could find on this NG and F150online archives, I decided to try replacing the #4 ignition coil, as that seems to be a fairly common culprit.
I'm not much of a mechanic, I'd never done much besides changing my oil, so I'm pretty happy to report that I seem to have solved the problem.
The coil was about $60 at Action Auto Parts. It seems to be running great! I hope it lasts....
It sounds like the #4 coils goes bad fairly frequently. Anyone know why? Heat or moisture? Any ideas to correct/prevent this?
-- Josh