98 zj 4.0 weird surging on highway - JeepForum.com
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Unread 01-22-2013, 05:17 PM   #1
05kjsport
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2005 KJ Liberty 
 
Join Date: Nov 2012
Location: North Olmsted, OH
Posts: 79
98 zj 4.0 weird surging on highway

Has anyone experienced a surging while at highway speed? It feels like a trans slip but the trans shifts fine from a dead stop to top gear. It seems to me the trans is shifting in and out of OD at highway speed after driving for awhile on the freeway, it also seems to me that OD kicks in earlier than it should as I am merging onto freeway getting up to speed it shifts fine through all the gears then hits overdrive too early and falls on its face, if i get more into the throttle it will kick down a gear as it should but then shift back into overdrive too early I think. Anyone had this issue?

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Unread 01-22-2013, 05:31 PM   #2
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 6,340
You may be feeling the torque convertor clutch lock / unlock. This occurs at around 45mph during normal acceleration when OD led is off.

If you are seeing a 100-300 rpm jump above 45mph, the brake switch is bad. You can confirm this by double footing, hold accelerator steady and lightly apply brake. If jumping stops, there's you sign.
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Unread 01-22-2013, 06:53 PM   #3
05kjsport
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2005 KJ Liberty 
 
Join Date: Nov 2012
Location: North Olmsted, OH
Posts: 79
I am seeing an rpm jump above 45, thanks zeejay will try that, is the brake switch a ***** to replace? Its under the dash attached to the pedal correct?
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Unread 01-22-2013, 07:09 PM   #4
ZeeJay1997
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1997 ZJ 
 
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Location: Sweet Home, Alabama
Posts: 6,340
I've never changed one, but others say it's easy. Also cheap. Kinda like a date I had once... or twice...
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Unread 01-28-2013, 06:00 PM   #5
05kjsport
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2005 KJ Liberty 
 
Join Date: Nov 2012
Location: North Olmsted, OH
Posts: 79
New brake switch installed and it did fix my problem, thanks for the help.
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Unread 04-09-2013, 01:36 PM   #6
qxotic
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1998 ZJ 
 
Join Date: Feb 2013
Location: Golden, IL
Posts: 15
I am having the same problem.. but new brake switch did not fix it for me. Any other suggestions?

I don't think it has ever done it cruising less than 50 mph. It is just on occasion on fairly level or slightly sloped road... never observed it going up hills or down. It is very brief by the time you feel it and look down to see the tach jump it's over.

Thank you,
Daniel
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Unread 05-14-2013, 11:46 AM   #7
Goliath27
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1996 ZJ 
 
Join Date: Sep 2010
Location: Cleveland
Posts: 67
I had the same issue as you two but my problem went away after I cleaned the IAC and it drove fine after that. Until recently where it no longer shifted into OD.

Not sure if cleaning the IAC fixed it or not, or if the brake switch is connected to my OD issue.
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Unread 05-14-2013, 12:02 PM   #8
Octotat
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1995 ZJ 
 
Join Date: Oct 2012
Location: Chattanooga, TN
Posts: 57
I've been having the same issue, over 50 mph and only when I hit a bump. The brake switch makes all the sense in the world now that I think about it. I love this forum
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Unread 11-21-2013, 11:08 PM   #9
Goliath27
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1996 ZJ 
 
Join Date: Sep 2010
Location: Cleveland
Posts: 67
Not to bump an old thread for nothing, but I did find a fix to my problem which has already come back.

I had a bad Transmission output shaft speed sensor, and changing that fixed my issue with the surging.

But now, I have a new issue, it only does it on highway speeds in OD. Gonna have to change that brake switch now.
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Unread 11-22-2013, 12:14 AM   #10
NewtoZJ
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1998 ZJ 
 
Join Date: May 2012
Location: Columbus, Ohio
Posts: 197
Mine does this occasionally. Might have to look into it after my laundry list of do's is whittled away.
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