Intermittent misfire on one cylinder - JeepForum.com

 
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post #1 of 6 Old 06-13-2012, 05:50 PM Thread Starter
Kalali
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Intermittent misfire on one cylinder

I had a misfire on cyl 4 code on my 2000 XJ along with all the symptoms of a cracked head. I went ahead and replaced the head with a Clearwater unit but I'm still getting the code but not all the time. Went ahead and switched injectors thinking maybe the injector was at fault. The code popped up but again not all the time. The engine runs the same with or without the code and the oil pressure is perfect cold or warm.
Could it be the harness or the connector or I have a bad coil rail? I know I asked this question before but shouldn't a bad coil set a pair of misfire codes not just one? I'm really stumped. Appreciate any guidance from the experts.

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post #2 of 6 Old 06-13-2012, 05:59 PM
tjwalker
It's the crank sensor!
 
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With cylinder 4 misfiring, yes it could be related to the head issue.

What exactly is your oil pressure at HOT idle and over 1600 rpms. The spec is as follows:

*Not less than 13 psi at HOT idle

*Between 37-75 psi over 1600 rpms

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Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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post #3 of 6 Old 06-13-2012, 06:03 PM Thread Starter
Kalali
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I was hoping you'd respond...
But I have a brand new head in there. That's what is stumping me.
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post #4 of 6 Old 06-13-2012, 06:04 PM
tjwalker
It's the crank sensor!
 
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Quote:
Originally Posted by Kalali View Post
I was hoping you'd respond...
But I have a brand new head in there. That's what is stumping me.
You may have a new head, but the old head may have done some damage to that cylinder. Top end damaging bottom end. A cylinder "leakdown" test is really the best comprehensive test for isolating single cylinder problems.

How long do you think you ran the engine with the cracked head?

Unfortunately, replacing the cylinder head is not going to remedy any issues that cylinder created with the bottom end of the engine. It really is not that uncommon.

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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post #5 of 6 Old 06-13-2012, 06:37 PM Thread Starter
Kalali
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Thank you for your response. I only put a few miles on the motor, not sure exactly how much but maybe a few hundred, after I discovered the low coolant.
So technically speaking, what is causing the misfire? When you talk about issues with the bottom end of the engine, are you saying there is lower compression in cyl 4 that is causing a misfire?
I'm an engineer by trade so I'm really intrigued. I'll read up on it in the meantime...
Thanks again.
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post #6 of 6 Old 06-22-2012, 02:01 AM
toninorini
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I had the same code come in on my 01. It was also slow to start. It turned over just fine but it wouldn't turn on for about 15 seconds. Turned out my fuel pump had a bad valve and all the fuel was leaking back into the tank from the fuel lines after it was off for the night. And since there was no fuel it gave me the cylinder one misfire. After the pump was replaced I no longer had he problem.
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