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Unread 05-20-2006, 10:21 AM   #1
matts98ZJ
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??? Hesitation ????

When i pull off sometimes it seems like its going to die it spudders and back fires just a small amount then it goes like nothen is wrong. dont do it all the time...
Any Ideas would be a big help

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Unread 05-20-2006, 11:18 AM   #2
Varkyl
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Quote:
Originally Posted by matts98ZJ
When i pull off sometimes it seems like its going to die it spudders and back fires just a small amount then it goes like nothen is wrong. dont do it all the time...
Any Ideas would be a big help
I am having the same problem. It doesn't do it all the time but usually does it after it has been driven then parked for about 10 to 15 minutes and then driven again. And it only does it on the first acceleration and after it does the little sputter and pop it runs perfect.

One of these days I will look into it a little further and should have more info then.
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Unread 05-20-2006, 12:19 PM   #3
laxwarriors21
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Same thing happens to mine every once in a blue moon! So if yall figure out what it is, then let me know.
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Unread 05-20-2006, 12:42 PM   #4
97zjjeeper
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ya my jeep does that to start off then BLAAAAAAAAA nothing pop then off she goes
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Unread 05-20-2006, 03:15 PM   #5
ajmorell
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I have the same thing sometimes. Every now and then I will throw a code. I don't know what number it was but I had it ran to see what it said and it came up that my downstream O2 was having some goofy voltage deal, like it would alternate high then low. Basically what the mechanic told me is sometimes what would happen is it would get this bad voltage reading and tell the ECU that the engine was too lean so it would give it more fuel and it would then actually be running rich causing the hesitation. I believe he said this problem was caused by my crappy catalytic converter messing up my downstream O2 sensor or the wiring was corroded on the sensor, I can't remember which.
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Unread 05-20-2006, 03:30 PM   #6
greasefingers
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Thatís exactly how the O2 sensor works Ö it oscillates between 0.1 to 0.9 volts, in a sine-wave manor. Anything below 0.45 is lean (too much oxygen) and anything > 0.45 is rich. The upstream O2 sensor is used by the PCM to fine tune the air-to-fuel ratio. The downstream one only tells you when the Cat is spent.

I would concentrate in other areas for sluggish acceleration.
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Unread 05-20-2006, 04:38 PM   #7
matts98ZJ
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I have no idea. cleaned intake system from manifold to injectors. Only does it like someone say about driving then park for 15 min or so like if you going in to a store then leaving when you pull out it does it. the it runs great after that....
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Unread 05-21-2006, 09:20 AM   #8
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My mechanic told me that problem was caused by my cracked exhaust manifold. It went away when he welded it, but seems to have reared its ugly head again.
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Unread 05-21-2006, 10:28 AM   #9
doyll
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Quote:
Originally Posted by matts98ZJ
I have no idea. cleaned intake system from manifold to injectors. Only does it like someone say about driving then park for 15 min or so like if you going in to a store then leaving when you pull out it does it. the it runs great after that....
Could possibly be caused by a hot engine compartment vaporizing the fuel in the lines & rail when parked. (engine off, no fuel moving in lines & injector rail) After starting it will run okay on vapor/liquid mix until you hit the throttle, then it's squirting too much vapor and not enough liquid through injector (engine stumbles gasping for fuel) until liquid fuel replaces vapor in rail and injectors are quirting liquid. Then engine runs like nothing is wrong again. Until you park it and hot engine compartment does it again.

Easy way to test this would be to open your hood when you park and see what it does when you start and drive off in 10-15 minutes vs. hood closed under same conditions.
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Unread 06-13-2006, 11:17 AM   #10
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Quote:
Originally Posted by ajmorell
I have the same thing sometimes. Every now and then I will throw a code. I don't know what number it was but I had it ran to see what it said and it came up that my downstream O2 was having some goofy voltage deal, like it would alternate high then low. Basically what the mechanic told me is sometimes what would happen is it would get this bad voltage reading and tell the ECU that the engine was too lean so it would give it more fuel and it would then actually be running rich causing the hesitation. I believe he said this problem was caused by my crappy catalytic converter messing up my downstream O2 sensor or the wiring was corroded on the sensor, I can't remember which.
That is interesting. I have the same problem, and was constantly throwing a "too lean" code. But the funny thing is, it seems to have gotten worse sense I put a new Cat on mine!

Anyone else have any information?

Last edited by Invisible; 06-13-2006 at 12:29 PM..
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Unread 06-13-2006, 11:34 AM   #11
ajmorell
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Did you try replacing the upstream O2? That would be my next area to check out.
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Unread 06-13-2006, 11:43 AM   #12
reneveah
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this may be the cause, read http://www.wjjeeps.com/tsb_list.htm#1803103
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Unread 06-13-2006, 12:26 PM   #13
Invisible
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Quote:
Did you try replacing the upstream O2? That would be my next area to check out.
I did replace that. About a year and a half ago I think.

Cat, muffler, starter were in the last 3 weeks.
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Unread 06-18-2006, 03:46 PM   #14
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I think I may have found the problem. My Dad was searching Technical Service Bulletins on our library's website and found:

TSB number 18-02-98
Subject: Long Crank Times/Sags/Hesitation or Slow run Up
Date: 2/6/1998

It's for 96 ZJ's, but it may help everyone. (with the 4.0 anyway)

Condition: Long Crank times/sags (etc) after a cold drive-away start. This condition is caused by an ignition switch triggered reset of the Power Train Control Module (PCM) which caused adapitive memory loss in the PCM.

Diagnosis: Using the Mopar Diagnostic system (MDS) or the Diagnostic Scan Tool (DRB III) with the approriate manual, verify all engine/transmission systems are functioning as designed. If Diagnostic Trouble Codes are present, record them on the repair order....

Anyway it gives the repair procedure, but I guess you'll have to go to a Jeep dealership to get it done. So good luck to everyone, and I'll be calling the dealership tommorw.
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Unread 06-24-2006, 01:19 PM   #15
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Had the prodedure done today. So far so good. I will let you know if it comes back.
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