I have a 2003 F150 with the 5.4 and 145,000 miles. About 2 weeks ago I took my truck to my mechanic for my engine light, cylinders 3 and 4 had a misfire. I had coil packs 3 and 4 replaced, this was on Thursday 8/7, that next Monday my engine came on, cylinder misfire on 4, was replaced again Wednesday, 8/13, and at 11:30 p.m. on 8/16 the light came on once again. The truck runs really rough, but only on cold start ups and once I hit about 2,000 rpms it goes away. Any idea what could be causing this?
are you 100% positive its the coil on plug? instead of just replacing the coils, try swapping the coils with coils from cylinders that are operating propely. if the misfire jumps to a cylinder with the COP from cylinder 3 or 4, then the coil is bad. if not, then you have another issue. have you checked/changed the plugs? make sure the plastic clips for the COPs are plugged in all the way. every now and then one of my clips will slide off, plastic locking piece broke off. cheap plastic!
