Misfire?

etc1006

TJ Enthusiast
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Jan 8, 2017
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108
Location
Maryland
So when sitting before clinicals studying I would fire Lucy up every so often to keep battery from getting too low. A couple times she acted like she was misfiring. Gently revved a couple times and smoothed out. Was this the #3 injector heat soak?? I finally got a check engine light today. I'll run the code tomorrow.


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It could be, but I'm more curious to see what the code says. That will tell a lot!
 
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So when sitting before clinicals studying I would fire Lucy up every so often to keep battery from getting too low. A couple times she acted like she was misfiring. Gently revved a couple times and smoothed out. Was this the #3 injector heat soak?? I finally got a check engine light today. I'll run the code tomorrow.


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You only get heatsoak when the engine is hot, shut off briefly, then restarted.
 
More details... what model year, what engine, and exactly (!) what spark plugs were last installed into your Jeep? Brand & model number please.

I agree with the above comment that the misfire is unlikely to be caused by heat soak.
 
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Last time I had a misfire code on my Cherokee I replaced the spark plugs, it had been close to four years, and cleared the code and I didn't get it again.
 
I believe it's an 01 Sport that he has.
2001 is where spark plug choice becomes more important as running the wrong technology spark plugs will cause idle problems and misfires due to its waste-spark ignition system. These are the engines with the coil pack ignitions. Older engines with distributor caps and spark plug wires are not nearly as fussy.

Single-tipped platinum plugs, which only have the platinum coating on one side of the gap, are the wrong type to install and they will cause misfires and idling issues. Bad plugs for 2001 and newer 4.0L engines include most Bosch, Autolite AP985, or Champion 3034.

Plugs that work well in 2001 and newer 4.0L engines include double-tipped platinums (platinum on both sides of the gap) like the Autolite APP985 or Champion 7034. Another good plug is Autolite's iridium-tipped plug which is the XP985.
 
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Got P138 O2 sensor. I figured it was the vac leak code Dad used to get once in awhile from the rubber hose on left fender apron on the canister thingy. He looked for a replacement, but was unavailable. I did find a box with some misc stuff with a heater hose with a 90 degree bend of approximately the same size. Dunno if he had plans to put that in. The ends are taped (high temp electrical) up real well on the one in their right now.... I'm thinking the O2 sensor code may have been random due to me not running her long enough while I was sitting there.


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2001 is where spark plug choice becomes more important as running the wrong technology spark plugs will cause idle problems and misfires due to its waste-spark ignition system. These are the engines with the coil pack ignitions. Older engines with distributor caps and spark plug wires are not nearly as fussy.

Single-tipped platinum plugs, which only have the platinum coating on one side of the gap, are the wrong type to install and they will cause misfires and idling issues. Bad plugs for 2001 and newer 4.0L engines include most Bosch, Autolite AP985, or Champion 3034.

Plugs that work well in 2001 and newer 4.0L engines include double-tipped platinums (platinum on both sides of the gap) like the Autolite APP985 or Champion 7034. Another good plug is Autolite's iridium-tipped plug which is the XP985.

Not sure on last tune up. Knowing Dad he did do one. I'll poke around in the files at the house and see what I can find.


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