I recently purchased a 97 f150 with the 4.6., 94k miles. The check engine light was on ,bought a code scanner & found o2 sencer bad [ 1 of 4 ]. Replaced it, fun job!! Now light came on again, #3 misfire. working on solution. The 4.6 and 5.4 have two coil systems. One has a coil on top of each sparkplug for short called cops, and no plug wires.The other has 2 coil packs,,one for each side of engine with plug wires running to each plug. [4 coil & 4 wires per side.] Just from reading in these forums it sounds like both engines have a challenge to change spark plugs, especeally rear plugs [no room to work]. Another issue is heater core replacement! sounds like you have to remove intire dash to do it. IF you a doityourself kinda person you can save some money if problems occur, Or you pay at the staelership!
I hope this helps? PS fords like oem parts!