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Zach O'Neill

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Oct 31, 2021
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Glasgow, Scotland
Hi all, firstly apologies as I've posted about this issue a couple times and in different places but im still having issues and in need of some advice, and am hoping that by posting again it might gain a few new eyes and some new interest.

I recently picked up an 04 TJ 4L with the 42rle auto transmission. Upon driving it home about 6 hours from where purchased I noticed an issue where it lost power in what I could only describe as waves, it lost it then immediately came back and then lost it before coming back again and then was completely fine for about an hour before happening again. This doesn't happen as often however still does both on and off the motorway.

The other issue is that when it comes up to temperature (ive never experienced it when cold, it generally starts to present itself as soon as it gets up to temp) it has an extremely rough intermittent idle that often results in a stall if not shifted into neutral and reved to keep it going. I originally thought this was to do with driving at highway speeds as it lost almost all power after coming off the motorway when I first got it but gradually ive started experiencing the stalling rough idle more and more and most importantly not just after coming from high speeds.

Some times it won't happen at all, other times it happens every traffic light. Most of the time once its moving again its good to go when others it has a lack of power when moving off. The strange part is it can go at one set of lights and then clear driving say 50meters and then be fine at the next stop.

The steps ive taken so far, Ive checked for codes and had it read externally, 0 faults. Ive cleaned the IAC and tb completely, no change. I thought it could be fuel pump related but I thought the fact it would rev up on command and start first time every time made me stray away from this. I also considered a sticky/faulty lock up torque converter but the issue happens when the overdrive hasn't engaged and has only been driven at slow speeds, so I wasn't sure if this ruled that out as well. Vac lines would cause an increase in revs not a reduction so that rules that out. I know for a fact it had O2 sensors replaced a month before I bought it so could this be causing the issue? is there a surefire way to test these rather than just replacing all 4 in the hope it helps? Im trying to contact the garage that done the work and see what brand were installed. I had also considered a fault in the PCM but considering the seller stated it ran 100% before I got it I believe it could have been something wear related from the journey home rather than a more serious problem.

The reason for posting again if ive just been out a drive and had the usual wanting to stall at lights but I also had a complete lack of power, the jeep was moving but pushing the gas to the floor resulted in nothing. On top of this at idle it sounded like an old tractor engine spluttering. When retarted it started right up drove perfect for about a minute and then lost power again.

Im unsure but would presume all three of these issues are all connected to one thing?

what else would you all suggest to try? im at a loss at this stage, any help would be vastly appreciated, and apologies for both the long post and at the repeat post, its just difficult to diagnose and what makes it worse is im in the uk so there's a distinct lack of jeep specialists with the nearest being 3 hours drive.

thanks
zach
 
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Zach O'Neill

Zach O'Neill

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Joined
Oct 31, 2021
Messages
31
Location
Glasgow, Scotland
Couple of things come to mind and I'm thinking maybe a failing Cat or crank sensor but either way checking fuel pressure would eliminate a fuel delivery issue.
I had taken it to a shop to get them to test fuel pressure as its the newer style without the schrader valve, but he said he couldn't get the fault to replicate, typical. He however did test it at its normal idle and said everything looked correct from that side of things. In his opinion he thought if it had an issue it would be out of whack regardless of the fact happening or not. Its just frustrating there's no codes
 
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Zach O'Neill

Zach O'Neill

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This sounds like it could be PCM related, calling Mark @Wranglerfix would help you have a few new things to try.
Ill need to look into this, I had taken it to a PCM specialist but he said he opened one in the past and they have a gel coating on them so there's very little to test without really knowing what your doing which involves shipping it back stateside. so I was hoping it would be something different. The guy had said most likely it could be something electrical or sensor related so was holding onto that hope. The other difficult part is finding replacements for an export
 
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rasband

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Ill need to look into this, I had taken it to a PCM specialist but he said he opened one in the past and they have a gel coating on them so there's very little to test without really knowing what your doing which involves shipping it back stateside. so I was hoping it would be something different. The guy had said most likely it could be something electrical or sensor related so was holding onto that hope. The other difficult part is finding replacements for an export
I missed your location, I apologize. I would think Mark can still give you some direction to check.

Electrical sounds likely to me, which is usually either behind the valve cover (there's a stud the loom often rubs on) or going over the bell housing. Of course they can be any number of other places. I damn near pulled out my entire wiring harness chasing one down that was a combination of my fuel pump and PCM.
 
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Zach O'Neill

Zach O'Neill

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Oct 31, 2021
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Glasgow, Scotland
I missed your location, I apologize. I would think Mark can still give you some direction to check.

Electrical sounds likely to me, which is usually either behind the valve cover (there's a stud the loom often rubs on) or going over the bell housing. Of course they can be any number of other places. I damn near pulled out my entire wiring harness chasing one down that was a combination of my fuel pump and PCM.
Its just insanely strange that it ran 100% before I got it. The guy I purchased from seemed really genuine and went out his way to replace the battery and fix faulty door handles before selling so I doubt he was lying when he sold it to me
 
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JKP

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Warner Robins GA
If it runs ok cold, then acts up when at temp, suggests the O2 sensor(s). The PCM goes closed loop and uses the O2s to adjust mixture when at operating temp. No sure if your export may have 1 or 2, but the O2(s) in question are the ones above the catalytic converters. Only use OEM MOPAR or NTK, the OEM supplier.
 
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Zach O'Neill

Zach O'Neill

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Joined
Oct 31, 2021
Messages
31
Location
Glasgow, Scotland
If it runs ok cold, then acts up when at temp, suggests the O2 sensor(s). The PCM goes closed loop and uses the O2s to adjust mixture when at operating temp. No sure if your export may have 1 or 2, but the O2(s) in question are the ones above the catalytic converters. Only use OEM MOPAR or NTK, the OEM supplier.
The o2 sensor thing kind of made sense as they were replaced about a month before I got it but I was told it ran well after they were fitted. I need to get under and check the brand as soon as the weather allows, I just didn't know what else sounded plausible as im running out of things to try
 
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Jerry Bransford

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If it runs ok cold, then acts up when at temp, suggests the O2 sensor(s). The PCM goes closed loop and uses the O2s to adjust mixture when at operating temp. No sure if your export may have 1 or 2, but the O2(s) in question are the ones above the catalytic converters. Only use OEM MOPAR or NTK, the OEM supplier.
X2 to the above. Exactly. I'll only add NGK as a 3rd alternative O2 sensor brand, NGK is exactly the same product as the NTK is, they even share the same model numbers. NGK owns NTK and is another channel of distribution for NTK.
 
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Zach O'Neill

Zach O'Neill

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X2 to the above. Exactly. I'll only add NGK as a 3rd alternative O2 sensor brand, NGK is exactly the same product as the NTK is, they even share the same model numbers. NGK owns NTK and is another channel of distribution for NTK.
Ill defiantly check the o2 sensors as soon as possible, one of the main automotive part suppliers in the uk is called Euro Car Parts, and they state the Bosch sensors as a part for the 04 wrangler, and given the garage it had work done on it it in wasn't jeep specific and considering the rarity of old jeeps over here Its highly probable he didn't know any better and just fitted what was suggested.
 
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Jerry Bransford

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Ill defiantly check the o2 sensors as soon as possible, one of the main automotive part suppliers in the uk is called Euro Car Parts, and they state the Bosch sensors as a part for the 04 wrangler, and given the garage it had work done on it it in wasn't jeep specific and considering the rarity of old jeeps over here Its highly probable he didn't know any better and just fitted what was suggested.
DEFINITELY (!!!!!) avoid Bosch O2 sensors. Yes Bosch is a good brand name but Bosch O2 sensors are well known to NOT work well in our Jeeps. Really.
 
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JKP

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BTW, that also goes for the spark plugs. No idea what your options are, but Bosch tend to cause issues. You need either a reg plug, a double plat plug, or an iridium plug for the coil rail ignition. NGK, Champion, Autolite all work well.
 
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Zach O'Neill

Zach O'Neill

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Oct 31, 2021
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DEFINITELY (!!!!!) avoid Bosch O2 sensors. Yes Bosch is a good brand name but Bosch O2 sensors are well known to NOT work well in our Jeeps. Really.
Ill check the brand that was installed as soon as possible. Do you think in your opinion something as simple as an o2 sensor could cause such the variety of issues I've been experiencing?
 
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Zach O'Neill

Zach O'Neill

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BTW, that also goes for the spark plugs. No idea what your options are, but Bosch tend to cause issues. You need either a reg plug, a double plat plug, or an iridium plug for the coil rail ignition. NGK, Champion, Autolite all work well.
I don't have a clue when they were last changed, I know jerry swears by autolite but getting the correct ones in the UK is sometimes quite difficult and quite costly. So ive got a full set of NGK ZFR5N ordered to get installed.
 

JKP

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Yes, as they control the mixture.

Also, if you have the 2 mini cats on the side of the engine, their mounting bolts can loosen and cause all kinds of drivability issues.

You can access the 4 bolts from underneath the Jeep with a socket and extension on a ratchet. Mine are 15mm but I have heard other years used 14mm.
 

JKP

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I don't have a clue when they were last changed, I know jerry swears by autolite but getting the correct ones in the UK is sometimes quite difficult and quite costly. So ive got a full set of NGK ZFR5N ordered to get installed.
Those are fine, you just have to change them every 30K miles or so.

The Autolite double platinums will go about 100K mi and the iridiums about 200K or so.