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Random inconsistent miss issues

LedSled

NAXJA Forum User
Location
Central Texas
I’ve been having problems with a miss that comes and goes here’s what’s going on. It’s 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. Wasn’t 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 it’s rough.

So here what I’ve 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.
 
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
 
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.
 
Also take a meticulous look at the wires that make up your injector rail harness, that's where it all started with my 2k.
 
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.
 
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.
 
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.
 
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.
 
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 here’s 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 that’s my issue. Would replacing the plug work? Or am I looking at a whole wiring harness.
 
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.
 
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.
 
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.
 
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.

Easy there. I'm just pointing out that the quality of aftermarket parts sucks. People who don't realize this can actually cause themselves more headaches when they start blindly replacing parts with poor quality replacements. There are plenty of examples on this forum of new parts being bad right out of the box, and the person thinking "well that can't be the problem because it's brand new".
 
Alright so I went and bought a noid light set to confirm what I thought was the issue but noid light is blinking as it should be so now I’m back to square one
 
Alright so I went and bought a noid light set to confirm what I thought was the issue but noid light is blinking as it should be so now I’m back to square one

How's the wiring look where it transitions between the engine to the firewall? It's not uncommon for the wiring to become chaffed or frayed inside, particularly if the motor mounts are bad. Often it shows up only when the engine moves during acceleration. I'd wiggle and shake that harness and see if it stumbles at idle.
 
^^This. It is a known issue . The injector harness will chafe where it bends around the fuel rail.
 
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