2003 Jeep misfire - Engine ODB2 Fault Codes


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2003 Jeep misfire

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Auto Repair Home>> Automotive Repair>> Engine ODB2 Fault Codes

mw1871
User

Nov 20, 2009, 5:09 PM

Post #1 of 3 (5019 views)

2003 Jeep misfire	Sign In

Hello to all, well here goes. I know this is long winded but I think it is all pertinent information. 2003 Jeep Grand Cherokee, automatic, 4.0 liter, 4x4. A couple of months ago the car was running rough so I tuned it up. The plugs were deffinately worn out. After the tune up she ran fine for a week then developed an occasional miss at idle only. When accelerateing she runs great. Well as time went on the miss got more frequent and finally set a code. ( #3 cyl misfire, I dont recall the exact p code) So I removev the coil pack and spark plug for inspection. No fouling, gapped correctly, no cracked porcelin, no signs of arcing. Well as long as it was apart I got a new boot between the coil and plug and put it back together. She ran fine for 2 days and we are starting with the misfire again. I was thinking coil, but found out #3 and #4 are fired from the same coil, and #4 is fine. I went to the library yesterday and surfed through the alldata site but could not find the diagnostics for the code. Yes the code was removed at the time of repair and the same code reappeared. I hope someone out there has dealt with similar issues so please give me so thought on where to look. Thank you to all and have a safe and happy holiday season.

Loren Champlain Sr
Veteran / Moderator
Loren Champlain Sr profile image

Nov 20, 2009, 6:23 PM

Post #2 of 3 (5007 views)

Re: 2003 Jeep misfire	Sign In

mw; Good to know, at least, which cylinder is causing the problem. The DTC that you got should be P0303? Assuming that it is not the plug which could be defective, the insulator, or the coil, anything is possible.

Could be a vacuum leak on that particular cylinder, or a dirty/plugged/faulty injector. Injector cleaner is 'okay' between actual cleanings, but won't clean up one that is plugged or a poor spray pattern. The fuel injectors should be cleaned at 30-40K intervals. If you haven't had it done, you could look at it as needed maintenance. We've unplugged many an injector using a Motor-Vac fuel injection cleaner, which most shops have. Of course, the basics, like compression should be checked so that you aren't kicking a dead horse.

Loren
SW Washington

mw1871
User

Nov 20, 2009, 9:39 PM

Post #3 of 3 (4998 views)

Re: 2003 Jeep misfire	Sign In

Just so there is no confusion, the miss is only once in a while. As soon as it starts it usualy quits. If it were a coil wouldn't it affect both cylinders as 1 coil fires both #3 and #4? I will check some local shops for the injector cleaning service.

(This post was edited by mw1871 on Nov 20, 2009, 9:43 PM)

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