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  #1  
Old February 18th, 2021, 21:09
LedSled LedSled is offline
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Random inconsistent miss issues

Iíve been having problems with a miss that comes and goes hereís whatís going on. Itís a 2001 4.0l with 226k miles. Everything stock engine wise except for k suspension 4 hole injectors and heat shielding. All injectors are wrapped. Jeep was running good accelerated hard a few weeks ago and check engine light started blinking. Wasnít far from the house so I drove home and shut it off. Turned it back on and the check engine light was on but not blinking. Idled rough tho, so I ran the codes and got back a P0301 cylinder 1 misfire. A few hours later walked out started it up and drove again. Check engine light was still on but idle was not rough. Next start up check engine light was gone idled fine drove good. Was fine for a few days then on a 3hr drive, check engine light started blinking again halfway there and started stalling with acceleration. Pulled over shut it off turned back on. Idled fine check engine light there but not blinking. Now check engine light is intermittent and a lot of times it idles fine and sometimes itís rough.

So here what Iíve done.

Swapped number one and 3 injectors no change.

Pulled number one injector plug while it was idling rough. This did not affect idle. But pulling a different injector plug did effect idle.

Replaced number 1 spark plug. Still intermitent rough idle.

Could it be TPS? Or possibly CPS?

Coil pack was replaced less that 3k miles ago.

Lastly I noticed two other things. Seems to have a tapping noise when idle is rough, and also it seems to shift into OD too early.
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  #2  
Old February 18th, 2021, 21:10
LedSled LedSled is offline
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Re: Random inconsistent miss issues

Also was going to test my CPS according to another post I saw on this forum and noticed my plug is in a completely different place than others
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  #3  
Old February 19th, 2021, 04:47
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Tim_MN Tim_MN is offline
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Re: Random inconsistent miss issues

Genuine Jeep coil pack or a cheap crappy Chinese clone part ?

What brand and part number of spark plugs ? The 2000-01 are more particular about the spark plugs. My 2000 runs best with plain old Champion Copper Top or Autolite APP985.

My primary suspect would be the k suspension 4 hole injectors and any Chinese parts. I would also look at the cylinder compression and possibly suspect carbon buildup on the valves. There is a Jeep TSB about valve carbon.

The TPS and CPS are not likely suspects for the symptoms described, but they are easy to test anyways.
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Old February 19th, 2021, 04:56
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cruiser54 cruiser54 is offline
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Re: Random inconsistent miss issues

This^^.
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  #5  
Old February 19th, 2021, 06:27
RCP Phx RCP Phx is offline
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Re: Random inconsistent miss issues

Also take a meticulous look at the wires that make up your injector rail harness, that's where it all started with my 2k.
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  #6  
Old February 19th, 2021, 07:57
maxbraketorque maxbraketorque is offline
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Re: Random inconsistent miss issues

It may not be CPS, but with 226K miles, I would proactively replace it. Besides that its a matter of testing connections and swapping parts as the others have said.
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Old February 19th, 2021, 09:31
LedSled LedSled is offline
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Re: Random inconsistent miss issues

The coil came from autozone.
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  #8  
Old February 19th, 2021, 09:32
LedSled LedSled is offline
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Re: Random inconsistent miss issues

Quote:
Originally Posted by RCP Phx View Post
Also take a meticulous look at the wires that make up your injector rail harness, that's where it all started with my 2k.
Another thing I forgot about was that the number one injector plug was almost impossible to get off while all the others easily pulled off. In fact I broke the clip trying to get it off. Not sure if that has any relation.
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  #9  
Old February 19th, 2021, 09:33
LedSled LedSled is offline
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Re: Random inconsistent miss issues

Plugs are champion copper
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Old February 19th, 2021, 10:00
RCP Phx RCP Phx is offline
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Re: Random inconsistent miss issues

Quote:
Originally Posted by LedSled View Post
Another thing I forgot about was that the number one injector plug was almost impossible to get off while all the others easily pulled off. In fact I broke the clip trying to get it off. Not sure if that has any relation.
Very possible since heat caused my injector wires to cross-fire.
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  #11  
Old February 19th, 2021, 12:17
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Re: Random inconsistent miss issues

You could be looking at a wire resistance issue.

If the #1 injector wiring has heated up enough to alter the effort required to remove it from the plug I would be giving those wires and the terminals in the socket a critical look.
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Old February 19th, 2021, 16:37
LedSled LedSled is offline
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Re: Random inconsistent miss issues

Quote:
Originally Posted by Anak View Post
You could be looking at a wire resistance issue.

If the #1 injector wiring has heated up enough to alter the effort required to remove it from the plug I would be giving those wires and the terminals in the socket a critical look.
Okay so hereís what I found out I checked the resistance of every injector plug wire and got roughly 5.66 ohms on every one except the cylinder 1 plug. So I think thatís my issue. Would replacing the plug work? Or am I looking at a whole wiring harness.
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  #13  
Old February 19th, 2021, 20:44
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Re: Random inconsistent miss issues

I would certainly start with just replacing the plug. Far easier than the whole harness.

The trick will be figuring out how far back the damage to the wiring goes.

I would unwrap the wires for that #1 plug (if your wiring is like mine the injector wiring is wrapped in some sort of black electrical tape rather than the split loom that is used throughout the rest of the engine bay) and figure out how far back you have to go before the wires are pliable. Once you know that you know how much you need to pull from a junkyard donor.

Take an extra couple of inches so that you can stagger the splices for the two wires.

I strongly recommend solder and heat shrink over crimped butt connectors.
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  #14  
Old February 20th, 2021, 09:45
lawsoncl lawsoncl is offline
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Re: Random inconsistent miss issues

Quote:
Originally Posted by maxbraketorque View Post
It may not be CPS, but with 226K miles, I would proactively replace it. Besides that its a matter of testing connections and swapping parts as the others have said.

This doesn't sound like a CPS problem. Also, I wouldn't proactively replace a working oem sensor with a cheap chinese one. The "new" one is likely to have a shorter life span than the working original.
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Old February 20th, 2021, 12:26
maxbraketorque maxbraketorque is offline
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Re: Random inconsistent miss issues

Quote:
Originally Posted by lawsoncl View Post
This doesn't sound like a CPS problem. Also, I wouldn't proactively replace a working oem sensor with a cheap chinese one. The "new" one is likely to have a shorter life span than the working original.
Did I say cheap Chinese or suggest a low cost sensor? I'm sure some OEM CPS sensors last 300K+ miles, but the reality is that the OEM sensor can go bad without a hint of warning at much lower mileages, as it did with mine that only had 110K miles the vehicle. I agree that the CPS is not likely to be the cause of his issue and I even noted that in my response, but I was just trying to provide some potentially helpful advice. I'm beginning to think that I choose the wrong forum to discuss XJs.
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