Rough Idle and misfiring -
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Go Back > Models > Jeep Grand Cherokee & Commander Forums > WJ Grand Cherokee Forum > Rough Idle and misfiring

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Unread 11-16-2014, 01:38 PM   #1
Registered User
1994 YJ Wrangler 
Join Date: Mar 2012
Location: Oxford, Ohio
Posts: 51
Rough Idle and misfiring

I purchased a 2002 Jeep Grand Cherokee 4.0 last winter and I've had constant issues with it even after putting a different engine in it. I've talked to several people and had it at a mechanic and no one can seem to figure out what is wrong with it. HELP!

A little background history.. In the original engine, the electrode fell out of the spark plug and put a whole in the piston, which in return messed up the cylinder. I purchased another motor that had a cracked piston skirt for $100. I fixed the piston and went through the rest of the motor and put new bearings, rings, gaskets on it. I put the engine back in and it still not running correctly.

It runs smooth at times (not very often, but sometimes) but it seems that when it acts up it's like it only runs on a couple cylinders. It loses power and had trouble maintaining speed. It idles rough and jerks every once in a while like it is running out of gas. It has been sucking the gas. I put $15 in an 30 miles it was on E again. I did notice that the temperature is staying on about 150 degrees when being driven so I'm going to put a new thermostat on it. The mechanic said that # 1 and 6 are showing a dead cylinder. All sensors have check out fine, the fuel pressure is good, and compression is good. I've replaced the injectors in 1, 5 & 6. The catalytic convertor was glowing red and clogged so I cut them off, beat the honeycomb out, and welded them back up. Today, I reset the computer and it ran fine for a while, but started acting up again. If I turn the Jeep off and turn it back on the problem goes a way (for a few miles). I'm completely stomped on this... anyone have any ideas?

Bshearer25 is offline   Reply With Quote Quick reply to this message
Unread 11-16-2014, 08:30 PM   #2
Registered User
2002 WJ 
Join Date: Jan 2012
Location: Orange county, CA
Posts: 832
Check the wiring harness feeding the coil rail where it curves around the back of the head/valve cover...make sure no wires are frayed.
Also...maybe the coils are bad on 1 & 6 .....replace coil rail...

Was the donor 4.0 out of a 2004 GC? ....and if so did you "carry" it's coil rail over to your 02? ..if so..that's your problem...need to keep 02 coil rail for 02 PCM....04 will fit but not work properly.

This is off an 01 it will work fine:
new2site is offline   Reply With Quote Quick reply to this message

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