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  #25  
Old 12-03-2012, 12:51 PM
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Re: '04 WJ, bizarre misfire of sorts

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Originally Posted by Lhutter1 View Post
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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The before cat O2 sensors should give a quite unstable voltage reading (with engine on), the more going up and down, the better the sensor is. If it shows a steady voltage or small differences, its time to change it.
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  #26  
Old 12-03-2012, 01:19 PM
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Re: '04 WJ, bizarre misfire of sorts

The readings weren't steady, they jumped around a bit, but were tracking pretty close to each other. There were two sets of numbers per O2 sensor. The first number on each would jump all around, which, from reading looks like they're supposed to, and the second number was a little more stable , but changing some. My original thinking was that since they're tracking reasonably close together, they should be ok. Please correct me if I not thinking that right.

After talking to my friend with the shop, he suggested an induction cleaning, which includes a bottle of BG 44K in the tank. He claims it's like giving the engine really good an enema. Something we all could use now and then! lol He claims that if O2 sensors are just dirty it will clean them as well, so I figure it's worth a shot.

Thanks!
Lorne
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  #27  
Old 12-03-2012, 04:48 PM
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Re: '04 WJ, bizarre misfire of sorts

Quote:
Originally Posted by Lhutter1 View Post
The readings weren't steady, they jumped around a bit, but were tracking pretty close to each other. There were two sets of numbers per O2 sensor. The first number on each would jump all around, which, from reading looks like they're supposed to, and the second number was a little more stable , but changing some. My original thinking was that since they're tracking reasonably close together, they should be ok. Please correct me if I not thinking that right.
2 Sets of numbers per sensor? Was one set not for the upstream and the other one for the downstream sensor? The downstream sensors have normally more stable readings
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  #28  
Old 12-04-2012, 07:53 AM
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Re: '04 WJ, bizarre misfire of sorts

That's interesting and I hadn't thought of it. In the analyzer they're just labeled O2 sensor 1/1, 1/2, 2/1, 2/2. Hadn't considered 2 downstream as well. I'm taking it in to my friend's for the induction cleaning later today and I'll mention that to him and get his thoughts on it as well. I did put in BG 44k last evening. Yesterday we also did an injector balance test and there was a notable difference in shutting down each injector. If none of the above works, next step may be pull the fuel rails and activate each injector to check spray pattern. Running out of stuff to try...

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  #29  
Old 12-04-2012, 06:45 PM
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Re: '04 WJ, bizarre misfire of sorts

Your WJ has two O2 sensors on each bank(right and left side of the engine) for a total of 4. The first sensor is before the converter and is used by the PCM to monitor the fuel mixture. The second is located after the catalytic converter to monitor the converter and ensure it is doing its job. I changed the pre-cat sensors on bank 1 & 2 after reading that over time they become less accurate. I also used the factory brand (I forget which brand) as my reading told me the other brands are problematic.
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  #30  
Old 12-05-2012, 07:36 AM
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Re: '04 WJ, bizarre misfire of sorts

Thanks for the clarification. We'll definitely be looking into O2s, sounds like a reasonable thing to change.

Last evening we did an induction cleaning and, though it's still not quite right, it seems to be better. One thing we did notice is the fuel pressure is steady at 47 lbs, ignition on but not running, on and at idle and high throttle. I seem to remember reading somewhere the spec being 50 lbs. How critical is that number?

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  #31  
Old 12-05-2012, 10:51 AM
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Re: '04 WJ, bizarre misfire of sorts

One more thought in light of your fuel pressure question... The WJ has two fuel filters. One sock-type is located in the tank on the fuel pick-up. The second is located over the rear diff and has an internal fuel pressure regulator. My hours of reading revealed that the regulator can become less accurate over time. I replaced the external filter/regulator while I will doing my 80k mile service. IIRC that filter was about $25. Rockauto.com has them anywhere between $15 and $30.
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  #32  
Old 12-05-2012, 11:04 AM
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Re: '04 WJ, bizarre misfire of sorts

Ah, good catch! I thought the only filter and regulator was in the tank (less than happy thoughts about changing that! lol). That's an easy thing to change.

I'm not sure how related it is to the stumble/misfire problem, but I have noticed the last week or so, that at cold start there's a little hesitation in the pedal, as if the choke wasn't set quite right (back in the days of manual choke). It doesn't feel like a misfire at that point, but I do have to play with the pedal a bit to accelerate. The colder it is, the worse it is. After a couple minutes of running that issue goes away.

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Lorne
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  #33  
Old 12-05-2012, 12:41 PM
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Re: '04 WJ, bizarre misfire of sorts

Been thinking about all the things I have changed on my WJ since I got it in light of my extensive WJ research. It seems you have covered most of them but here is my list for reference:
-Plugs (HO so I replaced the platinum plugs with the same ones)
-External fuel filter/pressure regulator (from napa)
-Throttle position sensor (Mopar)
Those three made a significant improvement in drivability and fuel economy at 80k mile.
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  #34  
Old 12-05-2012, 01:40 PM
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Re: '04 WJ, bizarre misfire of sorts

I did change the plugs, but with NGKs. It did not make a difference in the problem. I do have Champions ready to install, just to get it back to original. I've heard some say that other plugs just don't perform quite the same. I also changed the TPS. It's not a Mopar one. I've heard that can make a difference. Seemed to track the throttle OK with the analyzer, but could still be issue. Fuel filter is cheap and makes sense after 84k anyway. Will have to wait til the weekend to do that one.

Here's what I have done to date...
TPS
IAT sensor
IAT Harness
Plugs
2 coils (bounced them around different cylinders)
Air Filter
BG 44K
BG Induction cleaning
Pulled IAC and spray cleaned along with throttle body

Testing:
Fuel Pressure
Fuel Injector Balance
Disconnected coils one at a time
Used analyzer to view and test as many thing as I could

In the back of my mind I'm wondering about vacuum as well. There's nothing obvious, but along with changing the filter and such, I may start spraying around with carb cleaner or propane or something of the sort.

Thanks!
Lorne
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  #35  
Old 12-05-2012, 03:51 PM
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Re: '04 WJ, bizarre misfire of sorts

Regarding the fuel pressure, the manual states 49.2 +- 5 PSI, so yours is still within specs. Although i still think its a good idea to change that filter/regulator once in a while, just to avoid problems.
And regarding the O2 sensors, they are OEM from Denso. Eventhough Bosch is making very good O2 sensors, they heat up more slowly then the Densos and for that reason the PCM will set a DTC.
Just put today my jeep on a scanner and when i was doing some of the available tests, i found out that both precat O2 sensor heaters didnīt pass the test. Didnīt get any DTC for that nor higher then normal fuel consumption (ok, that normal is in fact already high ), but i will probably order some new sensors next time i do need something.
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  #36  
Old 12-07-2012, 08:00 AM
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Re: '04 WJ, bizarre misfire of sorts

Any more updates, Lorne?
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