96 ZJ issues once warmed up - JeepForum.com

 
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post #1 of 10 Old 09-14-2013, 02:26 PM Thread Starter
Hani96zj
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1996 ZJ 
 
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Location: Pearland
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96 ZJ issues once warmed up

Hello, thanks to all that assisted in my previous issue. Ok so the new issue is once my 96 ZJ 4.0 is at full operating temp it develops hesitation under load and will buck and bog at WOT. I have new plugs, tps, fuel filter, both O2 sensors and cleaned throttle body. When the jeep is cold runs normal and strong, once its warmed up it will not go WOT only bucks and bogs down until i let off a little.
I am really not sure where to look now? Would the MAP sensor cause issues like this? Fuel pump seems ok and it starts fast.

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post #2 of 10 Old 09-14-2013, 04:04 PM
Oldfrog
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Disconnect the upstream O2 sensor and try it.
What brand of o2 sensors?
NTK ?

2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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post #3 of 10 Old 09-14-2013, 04:16 PM Thread Starter
Hani96zj
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I have not tried that yet, the sensors are bosch. So what should i look for when testing this? Thanks
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post #4 of 10 Old 09-14-2013, 07:20 PM
ZeeJay1997
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post #5 of 10 Old 09-14-2013, 07:44 PM
Oldfrog
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Quote:
Originally Posted by Hani96zj View Post
I have not tried that yet, the sensors are bosch. So what should i look for when testing this? Thanks
Just unplug it and warm it up, then see if it bogs and acts stupid. If not...it was the Bosch sensor. If so, we look into other things.

My initial thought was TPS, but since it seems to work fine in open loop mode, I think we can eliminate that as a cause.

It wouldnt hurt to remove the coil and see if it's cracked on the back side, either. But usually a bad coil will eventually cause the PCM to kill the engine, not limit the revs....which brings us to Zeejays question...(assuming he thinks it's a timing related issue.)

2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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post #6 of 10 Old 09-14-2013, 08:00 PM
ZeeJay1997
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Quote:
Originally Posted by Oldfrog View Post
which brings us to Zeejays question...(assuming he thinks it's a timing related issue.)
I'm thinking clogged cat, but the things you mention are valid too
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post #7 of 10 Old 09-14-2013, 08:18 PM Thread Starter
Hani96zj
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Ok got it. I am going to try in the morning and report back. As far as valve noise, not that i can tell. Just seems like a rev limiter type bog.
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post #8 of 10 Old 09-15-2013, 03:55 PM Thread Starter
Hani96zj
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Ok guys tested. With the front sensor disconnected, i got the engine light but sypmtoms are not really as bad. I can actually go wot. Would it be safe to say ditch the bosch and order the NTKs?
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post #9 of 10 Old 09-15-2013, 04:41 PM
Oldfrog
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I would start with that, sure.
You can get them at Rockauto.com for about $47 for both of them, as I recall. Or you might try sending a PM to Kolak.

2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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post #10 of 10 Old 09-15-2013, 04:57 PM Thread Starter
Hani96zj
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Location: Pearland
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Thanks for the help. I will get them ordered.
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