Intermittent cylinder 4 misfire
- Thread starter Fistlaw
- Start date
How to Reset the ECU on a Jeep Wrangler JK
While there are folks that swear resetting your ECU does absolutely nothing, it's a common practice among automotive enthusiasts. The ECU (Electronic Control Module) "learns" your driving style and the parts in your ride by storing information in its memory, information that it gathers using a...
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WestCoastDan
JK Enthusiast
I recommend examining the wire harness at/around cylinder #4.
If you feel ambitious, consider swapping the plug and coil pack from #4 w/ another and see if the misfire remains on #4.
I would also consider doing a compression/leakdown test.
Although rare, I recently read a post stating that their misfire was the result of a crack in the head.
If you feel ambitious, consider swapping the plug and coil pack from #4 w/ another and see if the misfire remains on #4.
I would also consider doing a compression/leakdown test.
Although rare, I recently read a post stating that their misfire was the result of a crack in the head.
Threepointsix
JK Enthusiast
OP, whatever you do please keep us updated. This can truly help anyone that comes across the same issue @some point. Best of wishes! 
Well, it’s been a while but thought I’d follow up.
Cyl 4 has a valve that won’t close all the way so it’s not holding compression.
So after some serious emotion annd strings of four letter words coupled with disbelief, I’m going to pay a few grand to have it fixed. I’m all in and a new motor is too expensive, and a few grand isn’t even 6 months of car payments so…
I’m just shocked really. I bought her used with 70k-ish miles and don’t rag on it. I’m the second owner, but I’m absolutely shocked that an engine would lose a valve with only 93k miles.
Cyl 4 has a valve that won’t close all the way so it’s not holding compression.
So after some serious emotion annd strings of four letter words coupled with disbelief, I’m going to pay a few grand to have it fixed. I’m all in and a new motor is too expensive, and a few grand isn’t even 6 months of car payments so…
I’m just shocked really. I bought her used with 70k-ish miles and don’t rag on it. I’m the second owner, but I’m absolutely shocked that an engine would lose a valve with only 93k miles.
Threepointsix
JK Enthusiast
Very sorry to hear. Certainly beats buying another used Jeep that'll come with surely its own 'issues'. And new— I personally cannot stand the push button start and dual battery setup.Status update:
I found an engine specialist who’s torn down the driver side. The head needs replacing based on cost to fix vs getting a remanufactured one with a warranty.
Exhaust side valve leak confirmed.
While he’s in there I’m having him replace the rockers on both sides (a couple hours more labor+parts), and installing a Mishimoto aluminum oil cooler.
I found an engine specialist who’s torn down the driver side. The head needs replacing based on cost to fix vs getting a remanufactured one with a warranty.
Exhaust side valve leak confirmed.
While he’s in there I’m having him replace the rockers on both sides (a couple hours more labor+parts), and installing a Mishimoto aluminum oil cooler.