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  #13  
Old 11-14-2012, 10:58 AM
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Re: '04 WJ, bizarre misfire of sorts

Can anyone tell me what the resistance range should be of the IAT NTC? I remember checking it out of the vehicle a while back at around 45 degrees F ambient and the resistance was around 21k. I'm planning on replacing it with a pot to see if it makes a difference. Does that value seem within the range? If so I'll try a 50k pot...

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L.
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  #14  
Old 11-15-2012, 07:56 AM
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Re: '04 WJ, bizarre misfire of sorts

I put a 50k pot in place of the IAT sensor and did maybe notice a very slight difference. Seemed to be a bigger difference in idle stability. Not knowing what the resistance should be at 30 degrees made it a challenge and I really don't know if I was actually within range. I was able to see the voltage go up and down with the turning of the pot. At short circuit I do get a fault, as was pointed out I should. This evening I'm taking it to a friend's garage for a few other things and am going to hook it up to his scope to see what the PCM thinks while I'm there.

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Lorne
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  #15  
Old 11-20-2012, 07:38 AM
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Re: '04 WJ, bizarre misfire of sorts

Well, I never made it to my friend's shop over the weekend, however, I may have stumbled on to something else... As a side thought, I figured maybe a secondary on a coil was failing, so I picked up a coil and started playing leap frog with the coils, figuring maybe I would see different result if it was one of the coils. The problem never changed (so I thought). Later that evening we took it for a drive and I noticed that, though the loudish exhaust and vibration were still there, it was diminished by a considerable amount. Same thing the past couple of days. I'm wondering if I just moved the problem to a different cylinder or could I have had 2 weak coils and one is still weak? The IAT problem hasn't gone away, maybe a combinational problem? I think I need to make a coil tester to verify. Any thoughts?

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Lorne
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  #16  
Old 11-27-2012, 09:27 AM
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Re: '04 WJ, bizarre misfire of sorts

Hey guys!

Update: Ok, I made a harness and hardwired to the IAT sensor eliminating that connector. I used twisted pair wire to cut down on potential noise issues. I then cut the blk/red and blk/blu wires leading into the PCM about 2" back and spliced the new harness into it. Same results. It looks like the PCM is providing the voltage, but not responding to the changes in resistance. Anyone else thinking I need a new PCM? Other ideas?

Thanks!
Lorne
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  #17  
Old 11-28-2012, 07:39 AM
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Re: '04 WJ, bizarre misfire of sorts

OK, anyone that doesn't think I need a PCM?
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  #18  
Old 11-28-2012, 10:48 AM
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Re: '04 WJ, bizarre misfire of sorts

Hello? knock knock knock... Check 1-2... Hmmm... This thing turned on???
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  #19  
Old 11-28-2012, 10:57 AM
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Re: '04 WJ, bizarre misfire of sorts

When i donīt know, i prefer to keep silent then saying something that doesnīt help.
But if you insist: yes, buy a new PCM, it could be the problem. And if not, you just try something else.......
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  #20  
Old 11-28-2012, 11:07 AM
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Re: '04 WJ, bizarre misfire of sorts

Thanks Frank! I wasn't sure the posts were getting through. Thing's driving me batty! lol I do find though, that the colder it is out, the worse it runs, especially cold start now. Runs like the choke's not on enough and you have to play with the gas pedal a bit to accelerate til it warms up a bit. Never seems right though. Not sure if I have two problems at hand or just one that's being a PITA! I'll order a PCM Friday and see what happens!

Thanks again,
Lorne
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Old 12-03-2012, 09:53 AM
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Re: '04 WJ, bizarre misfire of sorts

OK, so I ended up borrowing my friend's scope/diagnostic tool to use while driving and learned a great many things. I don't think I need a PCM, here's why... The odd readings I've been getting on the IAT sensor are bogus numbers, actually from poor placement of the sensor. At cold start-up (which I had never tried the scope at) the sensor is within a couple degrees of ambient. As I would drive along, the temp would rise a bit. Sitting at a traffic light, the temperature where the sensor is located ran up to around 94*F. After my 20 minute drive on the highway it managed to get down to 20* above ambient, which was 52*F It never got all the way back down to ambient. If I let it sit and idle for any period, the temp would hover around 108*F (hence my high reading), even after shutting it off for a few minutes had the same results. So that knocks that out of running for real problems (other than design flaws lol).

I'm starting to wonder if it might be a flaky fuel injector? With a stethoscope of sorts, each one is clicking away just fine. Wondering though if one might be dripping or squirting instead of spraying nice getting worse as it heats up? I've run Seafoam through a couple times. I don't think it would be totally dead, because if I disconnect any of them one at a time it makes it run worse, same with the coils. Anyone got ideas on how to test that portion of the injectors? Other ideas or directions to check?

Thanks!
Lorne
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  #22  
Old 12-03-2012, 10:17 AM
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Re: '04 WJ, bizarre misfire of sorts

It could be a clogged injector that has a poor spray pattern. I would suggest some BG 44K in the tank to clean the injectors. Speaking of BG 44K, I should put some in the WJ...

That being said... I would expect poor spray pattern to create a lean condition and the PCM to add fuel. Any idea how old the upstream O2 sensors are? Ever replaced the TPS? Both of those are problem areas on WJ's with the 4.7. I replaced both and noticed a considerable difference with mine.
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  #23  
Old 12-03-2012, 10:41 AM
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Re: '04 WJ, bizarre misfire of sorts

Hmmm... Never heard of BG 44K, but I'll look into it today. I changed the TPS a while back. Didn't change anything and looking at the scope it followed well as I played with the pedal, so I'm thinking it's probably ok. Hadn't thought about O2 sensors much. They were working and looked ok through my eyes on the scope, but in reality they may not be sending accurate data.

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  #24  
Old 12-03-2012, 11:29 AM
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Re: '04 WJ, bizarre misfire of sorts

BG 44k = BG Company

Recommended by Nissan/Infiniti and BMW for fuel systems.
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