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Old 01-31-2010, 09:18 AM   #1
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Arrgh.. Cylinder 6 misfire...

Hi all, first post here. have a little problem hoping for some input.

I have an 03 TJ 4.0L. Been running fine, no issues till recently.

I started it up till a few days ago and it sounded like it was running on 5 cyl. I pulled the 0306 code indicating Cyl 6 misfire and another code for an O2 sensor..
Then today I replaced the battery since the old one was not holding a charge. After I put the new battery in, I started it up and it ran great. Drove it up the street for some gas and parked it again.

Now I start it again today and its doing that misfire thing again. I also have a check engine light on. Since it seem like a sporadic thing I am wondering if I am dealing with an electrical issue, maybe the coil rail or a bad plug? Anyone experience something like this?

Thanks a lot!
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Old 01-31-2010, 09:59 AM   #2
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I had something similar, but mine occurred right after I changed my plugs, turns out the old anti-seize prevented the plug from grounding out properly... I would definitely check your plugs first since that's quick and easy, if its been awhile, I would just change them out while your there. Just make sure that you use the plain jane truck plugs, don't spend any money on platinum this or that as sometimes the platinum plugs will make it run worse. If the plugs don't fix it, it would most likely be the coil pack.

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Old 01-31-2010, 11:52 AM   #3
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yea i just had a problem like this the other day. i changed my plugs for 15 bucks and she runs like a champ now
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Old 01-31-2010, 03:52 PM   #4
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Thanks for the info, I'll check the plugs first. Hopefully its something simple..
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Old 01-31-2010, 05:36 PM   #5
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Mine was a bad fuel injector.
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Old 01-31-2010, 06:18 PM   #6
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I had a similar problem - and fixed it

The tune-up would be a great start. While you're checking your plugs, consider replacing the distributor cap & rotor. If you have any hairline crack in the cap, you will end up with moisture inside of the distributor, which will affect the timing. Corrosion on the contacts will delay the spark from actually reaching the plugs, giving you a misfire. My pickup truck was doing this for a while, and I just did the tune-up that it so desperately needed and its running like a champ. Things to check, (and likely replace if its been a while):
  • Plugs
  • Wires
  • Distributor Cap AND Rotor, (if you replace one, its good practice to replace both).

I was getting a similar engine code for the O2 sensor on the truck, and that has since gone away. It was sporadically turning on, especially when it was moist outside - thanks to that hairline crack in the distributor cap. Funny how so many problems and symptoms can arise from one simple problem.

Hope that helps.

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