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Old 08-15-2017, 05:54 PM
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2007 Unlimited X Misfire questions.

Just picked up a high mileage 2007 wrangler unlimited. It's a 2wd, that will be 4wd eventually, but I got it for a good price.

When I got it it had a miss under load, tried to drive it home and after 15 miles it turned into a constant miss.

Codes and issues
1. Codes p2308 and p0300 misfire codes and coil secondary C codes
2. Also codes for emissions guess from running with two cylinders not firing.

First attempt and results
1. Replaced coil
- no change
2. Replace wires and plugs
- no change

Noted issues and possible resolution
1. Getting no spark to the 3 and 6 cylinder
- Thinking PCM is the culprit now.

Questions
1. Does this sound like a bad PCM or something else?
2. Anything else I should look at?
3. Do I have to get the pcm programmed if I replace it?

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Old 08-15-2017, 07:41 PM   #2
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PCM is a common culprit.. but so is a battery on it's way out, cheap spark plugs/wires. I put a new coil pack from a box store in my 09 3.8 and it was worse than the old one lol. Mine ended up being coil pack.

I would get the battery tested, check ALL the fender grounds (loosen/retighten DO NOT MONGO THEM, they will break, ask me how I know lmao) while the batt is out, reseat the connectors on the PCM and TIPM (careful with that little tenderheart too!). If it still has issues, take it and pay the $80 to put it on the Jeep computer for a diagnosis.

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Old 08-15-2017, 08:00 PM
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Quote:
Originally Posted by MW2016 View Post
PCM is a common culprit.. but so is a battery on it's way out, cheap spark plugs/wires. I put a new coil pack from a box store in my 09 3.8 and it was worse than the old one lol. Mine ended up being coil pack.

I would get the battery tested, check ALL the fender grounds (loosen/retighten DO NOT MONGO THEM, they will break, ask me how I know lmao) while the batt is out, reseat the connectors on the PCM and TIPM (careful with that little tenderheart too!). If it still has issues, take it and pay the $80 to put it on the Jeep computer for a diagnosis.
Battery is in great shape and almost new. Everything else purchased were quality parts. Though about the crank position sendor as well, but not sure it would cause no spark or fire at all out of the coil for cylinder 3 and 6.

I haven't looked at the fender grounds yet, but will do. I hate to pay the local dealer anything, and last time I called for an oil change in my ram 2500 they wanted me to wait 3 weeks. If it comes down to it, I can drag it 65 miles south to a quality dealer and have them test it. They are good but expensive. Would like and prefer to fix it myself, but hate chassing electric ghosts.
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Old 08-15-2017, 08:11 PM   #4
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Originally Posted by Grandall1972 View Post
It's a 2wd, that will be 4wd eventually, but I got it for a good price.
Obligatory THEY MAKE 2WD JEEPS???

You might find this helpful when the time comes https://imgur.com/a/bOzqS
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Old 08-15-2017, 08:34 PM
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Quote:
Originally Posted by Grandall1972 View Post
It's a 2wd, that will be 4wd eventually, but I got it for a good price.
Obligatory THEY MAKE 2WD JEEPS???

You might find this helpful when the time comes https://imgur.com/a/bOzqS
Yeah, I know when I first saw it for sale I about fell out of my chair at the price, but then noticed no transfer case shifter. Still I paid the price of an ok yj Wrangler for this 4door jk. I'm happy, and it's easy to make 4wd.
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Old 11-28-2017, 06:42 AM   #6
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Did you ever resolve your misfire issue? I ask because my '08 is doing the exact same thing, no spark at 6 and 3 after replacing coil, plugs, and wires. I'm pulling the PCU tonight when I get home from work and bringing it to work tomorrow. I work in an avionics shop, and we're going to open it up and see what we can find. My guys fix airplane electronics so I'm sure we can handle Jeep electronics. I'll try to update tomorrow what we find.
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Old 12-13-2017, 07:42 AM   #7
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***Update*** My PCM was bad. I opened it up and found that one of the MOSFETs that drive the coil was burned. I ordered new MOSFETs from Mouser electronics and replaced all three. Installed the PCM back into my Jeep and it immediately fired up on all six cylinders. $12.00 to fix it including shipping. Unless you are experienced in fine solder work, I would recommend you get someone else to take this on if you want to try it.
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