Driving with a misfiring cylinder

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ShafferNY

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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.
 

kj924

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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.
 

ridenby

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I believe I would replace the coil.they are not too expensive,might save you in long run.
 

moparman

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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.
 

ShafferNY

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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. :D
 

tjkj2002

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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. :D
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.
 

ShafferNY

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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.
 

ShafferNY

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I think I understand now.

The coil drivers are PCM hardware, not software. When someone says drivers, I think a piece of software like in a PC.

Why would one of these coil driver work intermittantly if they are solid state componets? Wouldn't they either work or fail completely?

Is it possible there is a programming glitch in the software that runs these drivers?

When our KJ thru a P0305 code shortly after all the engine work was done the garage did a leak down test and said the mechanicals of the engine seemed fine. At that point they insisted it HAD to be software related and did the reflash. That did absolutely nothing since the CEL and P0305 code came right back on before we got out of their driveway.

Starting to sound like a bad PCM on ours.

BTW, I don't mean to hijack this thread, but it sounds like we have very similar problems with this misfire code that keeps coming back.
 
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tjkj2002

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I think I understand now.

The coil drivers are PCM hardware, not software. When someone says drivers, I think a piece of software like in a PC.

Why would one of these coil driver work intermittantly if they are solid state componets? Wouldn't they either work or fail completely?

Is it possible there is a programming glitch in the software that runs these drivers?

When our KJ thru a P0305 code shortly after all the engine work was done the garage did a leak down test and said the mechanicals of the engine seemed fine. At that point they insisted it HAD to be software related and did the reflash. That did absolutely nothing since the CEL and P0305 code came right back on before we got out of their driveway.

Starting to sound like a bad PCM on ours.

BTW, I don't mean to hijack this thread, but it sounds like we have very similar problems with this misfire code that keeps coming back.
Yep,the drivers are a simple on and off switch that is commanded by the PCM via the cam and crank sensors and other sensors used to control timing.
 

Simpleman

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Did they by chance check your fuel pressure. Low pressure (from bad pump) can cause multiple misfires.
 

Dave

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Each coil has it's own driver for the 3.7,same goes for the fuel injectors.The power for the coils and injectors are supplied by the ASD relay and the PCM provides the ground for the circuits(drivers).

So what you are saying is that the PCM has a seperate driver in it for each cylinder and only one driver could be bad affecting only one cylinder??

As for the ASD relay, can that also affect only one cylinder?

Dave
 

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