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


zeitgeist57

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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...

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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

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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.

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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.
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