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Unread 04-29-2012, 03:32 PM   #1
Patman8354
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Jerking 1-4th gears

I purchased a 99 TJ 4.0L 5 mt with 60k mi yesterday and thought I was getting a great deal. Until late last night when it started bucking violently front to back while I was driving. It doesn't always do it. It usually starts out with a few small jerks and then a strong increase until I push the clutch in and start again. It also has an intermittent rough idle. I know it just had a new distributor cap and rotor, plugs,wires, and steering box installed if that helps. Does anyone have any experience with this? I really hope it is nothing expensive.


Last edited by Patman8354; 04-29-2012 at 04:39 PM..
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Unread 04-29-2012, 05:24 PM   #2
Jeepsr4me
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Sounds like a CPS issue. I went to buy a wrangler a few years ago. I get there and test drive it, and it started what you describe. The guy said it only did it every now and again and was embrassed about it. I got it for 1000 less than his bottom dollar, drove straight to autozone and replaced the cps in their parking lot. Drove home perfectly never did it again..
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Unread 04-29-2012, 05:30 PM   #3
Mean Max
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Quote:
Originally Posted by Jeepsr4me
Sounds like a CPS issue. I went to buy a wrangler a few years ago. I get there and test drive it, and it started what you describe. The guy said it only did it every now and again and was embrassed about it. I got it for 1000 less than his bottom dollar, drove straight to autozone and replaced the cps in their parking lot. Drove home perfectly never did it again..
CPS? Or do you mean TPS?

Typically, a CPS will either function perfectly or not at all, while a TPS will most definitely cause a driveability issue.

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No one here knows what they are talking about. You should try Pirate 4x4 they will be happy to help you.

There is no situation that cannot be improved with a small but well-placed explosive.
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Unread 04-29-2012, 05:55 PM   #4
Jeepsr4me
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CPS.. I do know what is what. Fluke that I changed it, cause thats all autozone had in stock and I said might as well. The old one was over 140k miles on it.
Great write up here. http://www.4x4xplor.com/cps.htm

Quote:
For me, my Jeep wasn't throwing any codes and so I wasn't completely sure that this was something I needed to replace. What lead me to think that it may need to go was the fact that I now have over 120,000 miles on the odometer, I have already replaced my O2 sensors and still had various engine issues including a rough idle under specific conditions. Specifically, my engine would run very rough on cold mornings or after driving it a long time with the AC on, turning off the engine briefly and then starting it back up again. I had also experienced times when climbing up long highway hills the engine would run quite rough... almost as if it were misfiring. Now, I should tell you that things are better since installing a new CPS but my engine is still running far from perfect.

Anyway, this write-up should help you out if replacing your Crankshaft Position Sensor is something that you need to do.
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Unread 04-29-2012, 06:21 PM   #5
Patman8354
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Jeepsr4me- Were you throwing a code/CEL? Mean Max- Are the CPS and TPS easily accessed? If so I will probably just do them both.

Last edited by Patman8354; 04-29-2012 at 06:48 PM..
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Unread 04-29-2012, 06:27 PM   #6
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Originally Posted by Patman8354
Jeepsr4me- Were you throwing a code/CEL? Mad Max- Are the CPS and TPS easily accessed? If so I will probably just do them both.
Yes, they are easily accessible.

The CPS is located on the bellhousing, at about the 11 o'clock position if you were looking at the rear of the engine. It can be changed from top or bottom.

The TPS is located on the throttle body assembly. It can be changed by removing two small Torx head screws.

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Unread 04-29-2012, 06:37 PM   #7
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Ok. I think I am going to start with the TPS because it is the more inexpensive of the 2 parts. Is this something that I need to go to Jeep for or are the aftermarket parts just as good? Thank you so much. As this is my first Jeep I think I will need all the help I can get.
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Unread 04-29-2012, 06:42 PM   #8
Mean Max
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I use locally available parts from the parts store.

TPS



CPS



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Unread 04-29-2012, 06:49 PM   #9
Patman8354
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Thanks! I will let you know how it turns out tomorrow. All of my local parts stores are closed now.
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Unread 04-29-2012, 07:06 PM   #10
Jeepsr4me
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That write up I posted the link to has pics and everything. Look for a vacuum leak 1st. I am a pretty good auto mech so I take into account that all the little things have been done or I do them. Vacuum leak will cause issues, also bad plugs and wires and cap. Seen bad straight out of box. I test them BEFORE putting in. Easy to do with volt meter.
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Unread 04-29-2012, 10:33 PM   #11
Patman8354
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How much resistance am I looking for with a good sensor?
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Unread 05-01-2012, 04:31 PM   #12
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It looks like the TPS was in fact the issue. I replaced it and threw it on a scanner while I drove around and all the numbers looked good. Thanks for all of your help guys!
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Unread 05-02-2012, 02:24 PM   #13
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So now instead of doing it all the time randomly it just does it when its cold now. Is the CPS the next part I should check?
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Unread 06-22-2012, 04:55 AM   #14
johnxjeep
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It seems there are a lot of threads on this problem/subject so I will post to the latest one.
My jeep started acting this way so I replaced the TPS low and behold that did nothing to stop the jeep from behaving badley like this.( she is still acting like a spoiled brat)

Has anyone actually fixed the problem? The posts/threads I have read have not really found a solution for the issue.

Any thoughts ?

Thanks.
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Unread 06-22-2012, 08:51 AM   #15
Patman8354
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I am starting to think it is a possible idle air control motor. I will do more research this weekend probably.
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