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Unread 09-15-2014, 12:58 PM   #1
Westy701
Registered User
2003 KJ Liberty 
 
Join Date: Sep 2014
Location: Fargo, Nd
Posts: 1
Can't work out misfiring codes

Bought 2003 Jeep Liberty Sport from friend in June. Ran fine for two months, nonstop issues for the last three weeks we can not seem to work out of Jeep.

Started 3 weeks ago, I was out of town and Jeep overheated on my husband. Code said bad relay. Husband changed. Ran fine for a few days. He picked me up at airport and it started to overheat again. We drove home with heaters on but kept the temp gauge at mid point.

Vehicle was running very rough. I got check engine light and had code checked: errors were random misfire and cylinders 1, 5 and 6. Husband changed all six plugs and PCV valve.

Couple of days later temp started rising and no heat would come out of vents. Changed thermostat, now have heat and no overheating...yet.

Check engine light again. Error on 2 and 6. Bought new coils this morning. Store only had one on hand. So I changed out 6 since it seems to consistently throw codes. Still running rough. I would also hear a "click" or two when starting. I checked code on dash and found error on 6. Pulled out new coil and swapped with 3. Same problem on 6. Check engine light even flashes at times.

This vehicle is so easy to work on, but I am about to give up on it. Suggestions?

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Unread 09-16-2014, 05:37 AM   #2
Billwill
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2002 KJ Liberty 
 
Join Date: Jul 2007
Location: South Africa
Posts: 999
I hope when the thermostat was replaced all the air was burped out and only HOAT anti-freeze was used?

What exactly are the codes you are getting?
What plugs did you replace with...normal copper NGKs are what I see recommended most but I do not use plugs so would not know.

Misfire on a cylinder could be caused by bad fuel injector. You sure you are counting the cylinders correctly?
Could also be caused by a bad Crankshaft Position Sensor or Camshaft position Sensor....hopefully codes will show this up.

You need to measure the wiring coming from the PCM to each coil and injector...check for continuity of the leads, resistance of the coil/injector and very important that none of the leads register any form of a short to ground.....hope you have a good Multimeter!

The trouble with having a short to ground...lets say on cylinder 6 coil....is that it will blow that section of the PCM so even if you find and repair the short the PCM will have that particular Power Transistor blown and calls for a PCM repair/replace.

You can download the 2003 KJ Service Manual here if you do not have it already....tells you what to do about the codes and includes circuit diagrams.

http://www.colorado4wheel.com/manuals/Jeep/KJ
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Unread 09-16-2014, 07:50 PM   #3
02blue
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2002 KJ Liberty 
 
Join Date: Aug 2011
Location: Frederick, MD
Posts: 367
Watch your coolant level. When my fan relay went in traffic, I cooked my headgaskets. Blown headgasket can cause a misfire. If you see the coolant drop could be burning it (smoke) or dumping it into the oil (oil level will rise and it will look like a milkshake after running a bit). Blown headgasket can cause a misfire. Aluminum heads don't like to be overheated especially when mated to a cast iron block.
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Unread Yesterday, 07:21 PM   #4
streetglideok
Web Wheeler
2005 KJ Liberty 
 
Join Date: Jul 2011
Location: Colorado Springs, Colorado
Posts: 2,394
+1 to whats been said. Did you clear the codes after each attempted fix? The codes do not magically go away, it has no idea if it's bene fixed or not, so you must clear them. Make sure you ID'd #6 correctly. Did you do a compression test on all 6 cylinders?
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