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Unread 10-29-2009, 04:29 PM   #1
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Join Date: Oct 2009
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Transmission Problems

Hey fellow Jeep owners, my first post on this site! So here's the basics on my Jeep, it's a 99 4WD Selec-trac with 170K miles. Recently I've been having an issue where I reach a cruising speed and apply even pressure on the gas peddle so that I maintain constant speed. From time to time, not consistently, I feel the Jeep briefly slip and then it jerks again. I usually let the gas pedal go wondering what just happened and then resume my cruising speed. It usually doesn't happen immediately after it just happened but sometimes it'll go a day or two without happening. I put about 50 miles on it each day so I do drive a lot. I'm just hoping the trans isn't on its last leg. Any thoughts or suggestions? Any further details or pics anyone needs? The check engine light does not come on or has not been on. I stuck the engine code reader just for fun and everything came out ok.

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Unread 10-29-2009, 06:16 PM   #2
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I don't think it is your transmission.

It is probably your tps (throttle position sensor).

I had the exact same issue, the overdrive would go in and out at highway speeds. I lived with it for a little while and then got a CEL code for a TPS. Replaced the TPS and all is well.

I replaced mine with an advane auto unit, but you will see quite a few people had issues with them. If doing it again I would probably go for the MOPAR unit reading about the issues. That said, mine is going strong well over a year...
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Unread 10-29-2009, 08:02 PM   #3
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1993 ZJ 
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What speed are you cruising at? Is it possible that you are cruising at the magic speed where the tranny doesn't know which gear to be in (shift point)?
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Unread 10-30-2009, 01:38 PM   #4
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CrazyIvan888: it really varies, but so do the points the transmission switches gears at. I hope it's not my shift solenoids, I had those replaced last year!

cmonson: that sounds like it could be right for me too. Since it's inconsistent I don't think it's an equipment failure in the transmission since I'd notice that all the time but rather the problem exists in some electrical component that is on the brink of breaking. I need to find some guides on replacing the TPS. One question, did your Jeep stall on you at any point? I was in the grocery store parking lot last night where I was going maybe less than 15 and the Jeep was close to stalling.
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Unread 10-30-2009, 01:59 PM   #5
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1998 TJ Wrangler 
Join Date: Apr 2004
Location: , Southeast MI
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You can test the TPS to verify it is causing the problems.

The center terminal of the TPS is the output terminal.

With the ignition key in the on position, check the TPS output voltage at the center terminal wire of the connector.

At idle, TPS output voltage should be greater than .350 millivolts but less than 900 millivolts.

At wide open throttle, TPS output voltage must be less than 4.5 volts.

The output voltage should increase gradually as the throttle plate is slowly opened from idle to WOT.
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