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Unread 07-01-2015, 10:11 AM   #1
Timo_90xj
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5.9 cutting, sputtering, and engine stalling

Well.. I'm kinda out of ideas.

My niner did this once about half a year ago, where it first started to cut/ misfire/ sputter and eventually die when the engine had reached operating temperature. I had codes for both O2- sensor voltages being high. I reset the codes and no issues ever since - until couple of days ago.

I ordered new NTK O2- sensors, which I did not yet install. I read the codes, I had a front O2- sensor voltage high code. Reset codes, started driving and was reading live data from the OBDII- reader while driving. ALL parameters from the sensors, air/ fuel mixture, all looked good - even O2- sensor voltages with the old sensors.

So, the issues:
* Engine during warm-up period, runs 100% normal
* Engine reaching operating temp, starts to cut/ miss/ sputter, and eventually dies
* If you rev it up to 3k+ RPMs and skinny pedal deep enough, it runs more or less fine
* When it starts to act up, will not idle correctly
* If you shut off the engine, let it sit for a minute or two, fire up and start driving, it'll work fine from mile up to couple of miles, then it's the same crap again.

Seems to me engine is behaving ok when it is in closed loop mode, but in open loop mode it certainly is not. Jeep is undriveable. I will install the new O2- sensors, but I highly doubt a bad front sensor would cause an issue like this.. it's not running rich, A/F mixture is more or less at perfect ratio, as is everything else judging by the OBDII- live output.


I already got a suggestion from a local Jeep guru (has been working only on Jeeps for the past 20+ years, has his own workshop), that it is most likely a PCM issue. I do believe it's a possibility (dried-up capacitors), but I sure as hell hope it's not that..

Ign. cap & rotor, wires and spark plugs are in very good condition and fairly new (OEM quality parts used). Ignition coil and distributor are both original. All sensors that I can measure with a multimeter are giving correct outputs.


Any thoughts?

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1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...

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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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Unread 07-01-2015, 11:49 AM   #2
kg6mov
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Pisser.

Both times my pig has acted like that it's just needed a texas tune up or a real one. It definitely sounds like it's a closed loop problem so it should be sensor based. I would double check the wiring and maybe do the zip tie on the connectors or take a dental pick to the connector sleeves to make sure there's a good connection.

If you narrow it down to the PCM you can have the one out of my niner, but you'd have to get it reflashed/programmed for the correct country.
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I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
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Unread 07-01-2015, 11:54 AM   #3
PolkaPower
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Have you tried unplugging the 02 sensors and seeing if it's normal at op temp? That might prove it is indeed a sensor problem rather than a pcm issue. Or just narrow it down at least.
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Unread 07-01-2015, 03:21 PM   #4
CatSplat
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Quote:
Originally Posted by Timo_90xj View Post
Seems to me engine is behaving ok when it is in closed loop mode, but in open loop mode it certainly is not.
I think you have it backwards, O2 sensors are only polled during closed-loop. I agree that the first test would be to unplug the O2's (force open loop) and run open loop up to temp and see if it makes a difference.
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Unread 07-01-2015, 08:22 PM   #5
Timo_90xj
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Yeah, that's what I meant.

I'll check it out with the front O2- sensor unplugged, but as far as it's output voltage, it is giving readings on the right scale according to OBD2- live data. But, could be it's not showing up correctly..
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1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...

http://www.jeepforum.com/forum/f13/d...s-etc-1222317/


1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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Unread 07-02-2015, 11:10 AM   #6
Timo_90xj
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Well.. looks like it was the upstream O2- sensor after all I've never had a bad O2- sensor cause anything resembling this, so that's why I was kinda stumped on the symptoms.


I first tried unplugging the the connector, but that just made things even worse. Jeep started acting up also with a cold engine, and once it warmed up it was even worse. I unhooked my battery for a few hours to clear the adaptive memory on the PCM, and once I had installed both new O2- sensors, I cleared the diagnostic codes once more.

Took it for a test drive, up to operating temps and engine under all kinds of loads, idle and coasting - zero issues. I'll keep a close eye on how it's working for the next few days, if it's fine I'm pretty sure this was an easy fix
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1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...

http://www.jeepforum.com/forum/f13/d...s-etc-1222317/


1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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Unread 07-02-2015, 12:09 PM   #7
kg6mov
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Fingers crossed that it's fixed and you're good to go!
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1996 ZJ Green Laredo V8, 2.5" OME and Bilsteins, 33's, Holes drilled in the roof.
1998 ZJ Platinum Limited 5.9, Backyard parts fodder
1987 Mercedes 300D Turbo, the diesel daily, 30mpg in style

Quote:
Originally Posted by Texas ZJ1 View Post
I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
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