2003 F150 4.6L 4x4 E/Cab XLT
Got rough idle, apparent unfired fuel smell in exhaust and code shows P0308, Cylinder 8 misfire.

Finally warm enough (5 F, -15 C) to look under hood today. Got coil off, long tight reach ( apparently I don't have to take anything else out of the way?). But top came off of boot, had to remove it separately. No apparent split boot issues. Spring connection to coil has bit of corrosion (ideas to clean it with?), reminds me of battery type corrosion film. Bottom end of spring looks like bit of film (does dielectric grease almost look rubbery when it's old?).

My bigger question is how tight should the spring fit on the spark plug, as it seems a bit loose on the Motorcraft SP-493 (I know not the best) replacement. Gonna pick up a meter (lent mine to out of town buddy, not available) to check resistance across the plug terminals, understand it should be ~1.8 ohm or less. Should I get a reading from one of terminal ends to the spring?

thanks for comments.

Update - Got spark plug out, it was also a 493, pretty wide gap, gotta find my gap guage. Interesting, it had a coating type film around top of thread base, and some more blew out of hole with air hose. Also, threads on old aren't full length of base as new one is (i.e., more threads) but all other measurements same.

Stuck until I get my test meter and gapper. I have the anti seize (Motorcraft nickel) and the dielectric grease. Hopefully tomorrow.

 

Motorcraft plugs ARE the best replacement. Do NOT use antiseize, torque the plugs to 28 ft/lb.

The thread lengths have been changed, I don't know exactly when they made the change.

If the gap is that wide, sounds like it's time to change all of them. Also sounds like you need to replace at least one coil.

 

I agree, while the coils can "come apart" they aren't supposed to do that either during normal service. Means the boot is fitting loose, and might have a moisture induced misfire as a result.

 

So the new plug gap came in spec at 0.053, the old one was probably toast at 0.083 and not much of inner extension left. Appreciate the no antiseize advice. Agreed, time to do all plugs, had them since Fall, just didn't have time to do, but now have to.

Not sure about the coil comments. Just to be clear, I probably separated the boot myself as I turned the top of coil while trying to pull it out, was pretty tight under the fuel rail that I didn't adjust/move. The boot itself seems ok, no cracks, fit back on coil. Tested resistance across plug end terminals, get 1.1 ohm, isn't that in spec?

Not getting a resistance between either plug end and the inner spring connector, but should I?

 

You can't really static test a COP. It can have resistance in spec, but still fail under load.

 

Thanks for advice.

The Good - spark plug and coil back in, started up, no unburnt fuel smell, reset codes, idled for a bit, not rough as before, no codes after ~ 25 minutes idling. Unfortunately no computer read outs for coil I can get with my laptop and obdII-wifi connector (ELM 327 interface), only injector faults available to read for 1-8.

The Bad - broke top of coil bolt off, so coil just sitting on motor. Possibly enough bolt sticking out of head base to grab and hopefully remove, again tight area, but how much vibration risk is there in the short term (still pretty cold out here).

 

Broken Coil Bolt is in a bit tighter than I expected. Pliers and vice grips slipping, and don't want to break it in place. Any ideas for bolt extraction in this tight area?

 

Need a broken bolt extractor. Looks like a socket, but has a twist teeth corkscrew design inside

 

Thanks, but haven't found an extractor small enough for the 5mm bolt. Only found 8 mm and 1/4" and up. Tried cutting into top and using a Phillips screw driver but edges broke on the try, and picked up a bolt remover plier but it still strips. Didn't want to break it but may have to drill. It's only sitting there for now.

Only good news was I managed to change all my spark plugs without issue.