'98 F150 - 4.6L misfire on cyl. 8?

[zeitgeist57]

Neighbor has a nice F-150. 4.6L V8, 101k miles, and it just started missing. He bought an Actron scanner today and it sez that he has a miss on cylinder #8. He says that an indy shop did a tune-up last year, but he thinks they only replaced the spark plugs, not the spark plug wires. Looks to be original wires, original fuel injectors (orange top).

 

Any common 4.6L problems that can cause this miss? Thanks...

[TurboRust]

isnt that coil on plug? if so, its almost definitely a coil

 

easy way to tell..

goto cyl 8, unplug injector, does miss get worse? if not, not an injector

if wires:

lift up wire, can you hear spark jumping? does the misfire get worse?

If you hear no spark jumping, follow that wire to the coil pack, lift it there, do you hear/see arcing? if so, bad wire, if not bad coil

 

if coil on plug, unplug coil, does misfire get worse? if not, bad coil

[EvoXbmx]

I wouldnt be surprised if it was a spark plug. be very very careful pulling it, because they like to break in half when coming out!! crack it loose and spray lots of pb blaster in the hole, then work it the rest of the way out

[AJ]

prolly just needs a coil. very common on the 4.6l. IIRC the MSD coils from jegs are cheeper than the stock coils from auto zone or advanced.

[zeitgeist57]

I saw the coils...there are two, looks like one each for servicing 4 cylinders.

 

Derek, I'll give the fuel injector plug a try...seems like a quick way to eliminate the fuel problem in ascertaining whether air, fuel, or spark is the problem...

[spankis]

Man all these suggestions remind me of when I asked for troubleshooting help with my mom's suburban earlier this year. Thought it was a coil, then an injector, then plug wire....turned out to be lifter issue that had ruined the cam. What a cool deal that was....

 

Not at all suggesting that's the case here, I totally agree with coil.

[AJ]

oh this is the way old style. never mind what i said then.

[Richard Cranium]

Since it is only one cylinder it's probably not timing or air. Spark or fuel are next. If neither of those are the problem then try a compression test, could be a sticking valve not allowing compression.

[Sully]

My truck developed a miss this past spring. Granted, it's a 2004, but it turned out to be loose terminal nuts on a couple of plugs, which then fouled the coil packs on those 2 plugs.

[DOZZER]

Pull the wire out from the hole and see if it is wet. If the people that did the tune up didn't seat the boot correctly you can get water in there and cause a miss. If it is dry check for spark. If you have spark check the plug just in case if they didn't replace that one. If it is good move on to your injector and check to see if you have pulse. If you have pulse then swap injectors with another cylinder. If the miss jumps, replace the injector. If it doesn't change, do a compression test.

[Cordell]

I would check the plug and wire, then swap parts one by one between cylinders to narrow it down.

[Awfulcanawful]

If they didn't change all the plugs they probably left that one in for a reason and you may be in for a real headache getting it out.

[Dave1647545494]

I have an inline spark tester tool kit if you want to borrow it clay

[zeitgeist57]

Thanks everyone! CR Rocks! :thumbup:

 

Talked to him last night (f*n cold, I'm not helping him work on his truck!) and he happened to mention that the plug wire felt "gunky"??? Maybe water is a problem...