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Driving with a misfiring cylinder


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Old 05-27-2009, 06:03 PM   #1 (permalink)
 
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What are the long tern effects of driving a KJ with CEL on?

Our '06 has a cylinder three misfire and the dealer we bought it from told us it wouldn't hurt anything to keep driving the vehicle.

I've read that when there is an engine misfire the PCM shuts off the injector to that cylinder to keep from washing the bearings out, etc.

The engine definitely has a noticable vibration from the cylinder not firing. I believe that alone would do long term damage if driven excessively.

Oh. Here's the best part. The Jeep dealership that the they, the dealership we bought it from, wants to take it to is 70 miles away. What kind of damage may that cause?

I'm hoping this engine just blows up and then they'll have to replace it.
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Old 05-27-2009, 06:12 PM   #2 (permalink)
 
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I don't think a 70 mile drive will do any harm to the engine. Now if you were to drive across the country, then maybe, just maybe. But for a relatively short drive like that, it should be ok.

I drove mine this winter for a month with a cylinder misfire with no issues.
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Old 05-27-2009, 06:25 PM   #3 (permalink)
 
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I believe I would replace the coil.they are not too expensive,might save you in long run.
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Old 05-27-2009, 08:03 PM   #4 (permalink)
 
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Originally Posted by ridenby View Post
I believe I would replace the coil.they are not too expensive,might save you in long run.
I read the earlier posts, the coil had already been replaced, right? I really don't think the misfire would hurt the engine. If it were valvetrain related, it would just burn the valve a little more. If that were the case, there was already a problem anyway.

I wonder if it was in an accident and there was a ground wire missing or something like that... The PCM needs to be grounded well and the engine needs to be grounded to the frame. The battery needs to be grounded to the engine and the frame. Is it still the original battery? Sometimes a battery can make electrical noise that results in a bad diagnosis. I once had a battery cause bad driveability problems on a 69 Impala. I thought for sure that there was a problem with the distributor or carburetor but it wasn't. That was in the mid 70s, stuff like that you never forget.
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Old 05-27-2009, 08:40 PM   #5 (permalink)
 
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The fact of the cylinder not firing isn't much a concern. I'm more concerned about the excessive vibration tearing the engine apart.

Moparman,
None of the coils have ever been replaced with new ones.

When the problem first appeared, the first Jeep dealership it was taken to swapped the coils around and that made no difference. Then they put new spark plugs in it, even after I had just changed them.

They claimed that the Bosch Platinum spark plugs that I had put in were the possible cause of the problem, so they installed Champion Copper Core plugs. A short while after the problem resurfaced, proving the plugs were not the culprit.

Yes, the battery is original.

Other than change the plugs, I have not touched the vehicle myself.

I have the freeze frame data from the PCM downloaded on my computer and can post it here if anyone thinks they might be able to diagnosis the problem.
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Old 05-27-2009, 08:47 PM   #6 (permalink)
 
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I don't really want to start two threads, so I posted the freeze frame data over on here.
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Old 05-28-2009, 11:11 AM   #7 (permalink)
 
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Originally Posted by ShafferNY View Post
The fact of the cylinder not firing isn't much a concern. I'm more concerned about the excessive vibration tearing the engine apart.

Moparman,
None of the coils have ever been replaced with new ones.

When the problem first appeared, the first Jeep dealership it was taken to swapped the coils around and that made no difference. Then they put new spark plugs in it, even after I had just changed them.

They claimed that the Bosch Platinum spark plugs that I had put in were the possible cause of the problem, so they installed Champion Copper Core plugs. A short while after the problem resurfaced, proving the plugs were not the culprit.

Yes, the battery is original.

Other than change the plugs, I have not touched the vehicle myself.

I have the freeze frame data from the PCM downloaded on my computer and can post it here if anyone thinks they might be able to diagnosis the problem.
What plugs are in the engine right know? If you still have copper core plugs in it pull #3 plug,get out the spark plug gapper and reduce the gap to 0.035".Try that out,if the misfire comes back there are only 2 possibilities left since the coils have been switched around,a bad PCM coil driver or the head is still messed up.
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Old 05-28-2009, 11:28 AM   #8 (permalink)
 
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I know the PCM has been reflashed by the dealership at least once that I know of.

Yes the copper cores are still in there. I'd try that, but I don't want to touch it since the dealer is still covering it. I will mention it to them though.
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Old 05-28-2009, 11:33 AM   #9 (permalink)
 
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Originally Posted by ShafferNY View Post
I know the PCM has been reflashed by the dealership at least once that I know of.

Yes the copper cores are still in there. I'd try that, but I don't want to touch it since the dealer is still covering it. I will mention it to them though.
A reflash will not effect the coil drivers,they are solid state.
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Old 05-28-2009, 04:57 PM   #10 (permalink)
 
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Is there one coil driver in the PCM for each cylinder? Or are the coils fired 2 at a time?
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