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Unread 09-14-2013, 02:26 PM   #1
Hani96zj
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1996 ZJ 
 
Join Date: Aug 2013
Location: Pearland, Texas
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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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Unread 09-14-2013, 04:04 PM   #2
Oldfrog
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1997 ZJ 
 
Join Date: Feb 2008
Location: Louisiana/Texas
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Disconnect the upstream O2 sensor and try it.
What brand of o2 sensors?
NTK ?
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Unread 09-14-2013, 04:16 PM   #3
Hani96zj
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1996 ZJ 
 
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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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Unread 09-14-2013, 07:20 PM   #4
ZeeJay1997
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when it buck and bogs do the valves rattle?
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Unread 09-14-2013, 07:44 PM   #5
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.)
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"..it's not air, it is the opposite of air... suckage so to speak."
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Unread 09-14-2013, 08:00 PM   #6
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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Unread 09-14-2013, 08:18 PM   #7
Hani96zj
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1996 ZJ 
 
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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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Unread 09-15-2013, 03:55 PM   #8
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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Unread 09-15-2013, 04:41 PM   #9
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.
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Unread 09-15-2013, 04:57 PM   #10
Hani96zj
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Thanks for the help. I will get them ordered.
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