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Unread 10-21-2012, 01:28 PM   #1
neonhomer
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Location: Edgewater, FL, Florida
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96 ZJ 4.0 keeps throwing CEL and trying to die..

Short story - Motor rebuilt about 5k ago. Used a Comp 68-232-4 cam in the rebuild. Also used 703 injectors. Motor is stock otherwise.

Had a downstream O2 sensor go bad. Replaced it (Mopar sensor), and now I am getting a P0171 Bank 1 Lean code. The motor will almost die, then throw the check engine light, and then will try to idle back up.

Now it has started something different. Besides the P0171, it now wants to misfire at part throttle. I was driving down the highway at 70, and it was missing fairly regularly. I dropped out of OD and sped up to 80 (bringing the RPM past 3k), and it didn't do it. I fall below 3k and it starts missing.

The only thing I can think of is the cam is causing this, needing more fuel than the PCM is capable of delivering. Looking at the fuel trims, it is around -15 or so.

I have no way to remap this PCM, which is what I think I will ultimately have to do.... Unless it's just my upstream O2 going bad.

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[COLOR="Lime"][SIZE="5"]NeonHomer[/SIZE][/COLOR]
Mid-Florida Jeep Club - Member
1996 Jeep Grand Cherokee, 4.0L/42RE/242 - Rebuilt motor w/ Comp cam (4/12), 3.5" Junkyard F>R lift, 31x10.5.x15 M/T's, Spartan Locked D44a, TC & tank skids, F&R adj trackbars, V8 steering arms
Galaxy DX99V CB, 102" SS Whip, Yaesu FT-2900R 2m, Larsen 1/4w mag mount, Sony HU, Massive 3way - F Door, Pioneer 3way - R Doors, MB Quart ONX304 Subs (x2), Lanzar 1600w amp.

"No Matter Where You Go... There You Are."
"Oh me oh my a lovely day is dawning. Oh what a joy I didn't wake up dead. So I can go to work and then resume my yawning, and get my sleep on site instead of in my bed" - Daria Morgendorffer (with my twist)
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Unread 10-21-2012, 01:51 PM   #2
ratmonkey
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that's a code for the upstream sensor and the other symptoms point to that as well.
that cam looks like a solid mid level computer friendly cam.
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Unread 10-21-2012, 01:56 PM   #3
neonhomer
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So sounds like a safe bet to replace the upstream O2 and see what happens...
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[COLOR="Lime"][SIZE="5"]NeonHomer[/SIZE][/COLOR]
Mid-Florida Jeep Club - Member
1996 Jeep Grand Cherokee, 4.0L/42RE/242 - Rebuilt motor w/ Comp cam (4/12), 3.5" Junkyard F>R lift, 31x10.5.x15 M/T's, Spartan Locked D44a, TC & tank skids, F&R adj trackbars, V8 steering arms
Galaxy DX99V CB, 102" SS Whip, Yaesu FT-2900R 2m, Larsen 1/4w mag mount, Sony HU, Massive 3way - F Door, Pioneer 3way - R Doors, MB Quart ONX304 Subs (x2), Lanzar 1600w amp.

"No Matter Where You Go... There You Are."
"Oh me oh my a lovely day is dawning. Oh what a joy I didn't wake up dead. So I can go to work and then resume my yawning, and get my sleep on site instead of in my bed" - Daria Morgendorffer (with my twist)
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Unread 10-21-2012, 02:12 PM   #4
ratmonkey
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try the unplug trick first after a computer reset. just see what it does on only the base maps with no ltft adjustment.
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Unread 10-21-2012, 03:16 PM   #5
neonhomer
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Okay... Will see what happens....

I was sitting here thinking about it. The current sensor was in the Jeep with my old motor, and it was burning oil. Not a lot, maybe a qt every 3000 miles..
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[COLOR="Lime"][SIZE="5"]NeonHomer[/SIZE][/COLOR]
Mid-Florida Jeep Club - Member
1996 Jeep Grand Cherokee, 4.0L/42RE/242 - Rebuilt motor w/ Comp cam (4/12), 3.5" Junkyard F>R lift, 31x10.5.x15 M/T's, Spartan Locked D44a, TC & tank skids, F&R adj trackbars, V8 steering arms
Galaxy DX99V CB, 102" SS Whip, Yaesu FT-2900R 2m, Larsen 1/4w mag mount, Sony HU, Massive 3way - F Door, Pioneer 3way - R Doors, MB Quart ONX304 Subs (x2), Lanzar 1600w amp.

"No Matter Where You Go... There You Are."
"Oh me oh my a lovely day is dawning. Oh what a joy I didn't wake up dead. So I can go to work and then resume my yawning, and get my sleep on site instead of in my bed" - Daria Morgendorffer (with my twist)
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Unread 10-21-2012, 05:44 PM   #6
neonhomer
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Location: Edgewater, FL, Florida
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Unplugged the Upstream O2, and then reset the PCM. After about 10 minutes, the CEL tripped, like I knew it would. The code it throws is a P0132 Upstream O2S (1/1) shorted to voltage.

How in the hell does it do that if the sensor is not even there... It should be reading 0v, not 5v.... but the scanner says it is reading around 5v....

The fuel trims didn't do anything. They are staying at 0. I thought they would go to a default rich value. What's bad is I smell that damn rotten egg smell, which, IIRC, means its running really lean, and cooking the cat...

Anyway... new NTK sensor is on order. Will see what happens when I swap it out Tuesday.

I am wondering if my PCM is going haywire...
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[COLOR="Lime"][SIZE="5"]NeonHomer[/SIZE][/COLOR]
Mid-Florida Jeep Club - Member
1996 Jeep Grand Cherokee, 4.0L/42RE/242 - Rebuilt motor w/ Comp cam (4/12), 3.5" Junkyard F>R lift, 31x10.5.x15 M/T's, Spartan Locked D44a, TC & tank skids, F&R adj trackbars, V8 steering arms
Galaxy DX99V CB, 102" SS Whip, Yaesu FT-2900R 2m, Larsen 1/4w mag mount, Sony HU, Massive 3way - F Door, Pioneer 3way - R Doors, MB Quart ONX304 Subs (x2), Lanzar 1600w amp.

"No Matter Where You Go... There You Are."
"Oh me oh my a lovely day is dawning. Oh what a joy I didn't wake up dead. So I can go to work and then resume my yawning, and get my sleep on site instead of in my bed" - Daria Morgendorffer (with my twist)
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Unread 10-21-2012, 05:54 PM   #7
ratmonkey
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i would check the wiring for burnt areas and have a real close look at the connector. you've got a decent problem going on here.
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Unread 10-24-2012, 08:27 PM   #8
neonhomer
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New O2 in. Readings bouncing around like usual. A friend of mine came over and changed the sensor for me while I was at work, and he said he noticed a spot in the wire that looked funky, but he didn't do anything with it as he knows I am particular about my wiring repairs. (Crimp, then solder, then epoxy heat shrink)

I will crawl underneath it tomorrow and see. With the new O2, it's reading between Rich and Lean like it is supposed to, and adjusting the fuel trims like it should as well.
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[COLOR="Lime"][SIZE="5"]NeonHomer[/SIZE][/COLOR]
Mid-Florida Jeep Club - Member
1996 Jeep Grand Cherokee, 4.0L/42RE/242 - Rebuilt motor w/ Comp cam (4/12), 3.5" Junkyard F>R lift, 31x10.5.x15 M/T's, Spartan Locked D44a, TC & tank skids, F&R adj trackbars, V8 steering arms
Galaxy DX99V CB, 102" SS Whip, Yaesu FT-2900R 2m, Larsen 1/4w mag mount, Sony HU, Massive 3way - F Door, Pioneer 3way - R Doors, MB Quart ONX304 Subs (x2), Lanzar 1600w amp.

"No Matter Where You Go... There You Are."
"Oh me oh my a lovely day is dawning. Oh what a joy I didn't wake up dead. So I can go to work and then resume my yawning, and get my sleep on site instead of in my bed" - Daria Morgendorffer (with my twist)
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Unread 02-03-2013, 06:21 AM   #9
neonhomer
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Location: Edgewater, FL, Florida
Posts: 447
Just a quick update for those who have the same code... The new O2 sensor fixed it. Code went away, and the Jeep is running like it is supposed to.

I examined the wires to the sensor, and they all looked okay. I traced it back as far as I could and didn't find any damage.
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[COLOR="Lime"][SIZE="5"]NeonHomer[/SIZE][/COLOR]
Mid-Florida Jeep Club - Member
1996 Jeep Grand Cherokee, 4.0L/42RE/242 - Rebuilt motor w/ Comp cam (4/12), 3.5" Junkyard F>R lift, 31x10.5.x15 M/T's, Spartan Locked D44a, TC & tank skids, F&R adj trackbars, V8 steering arms
Galaxy DX99V CB, 102" SS Whip, Yaesu FT-2900R 2m, Larsen 1/4w mag mount, Sony HU, Massive 3way - F Door, Pioneer 3way - R Doors, MB Quart ONX304 Subs (x2), Lanzar 1600w amp.

"No Matter Where You Go... There You Are."
"Oh me oh my a lovely day is dawning. Oh what a joy I didn't wake up dead. So I can go to work and then resume my yawning, and get my sleep on site instead of in my bed" - Daria Morgendorffer (with my twist)
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