1990 Cherokee will not upshift (transmission? computer?electrical?) - JeepForum.com

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post #1 of 6 Old 09-25-2007, 01:15 PM Thread Starter
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2007 KJ Liberty 
Join Date: Dec 2004
Location: Pickerington
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1990 Cherokee will not upshift (transmission? computer?electrical?)

I drive a 1990 Jeep Cherokee, 4WD, 4.0L, automatic. It only has 80,000 miles on it but it drives weird. I have to get up to 35mph and 4200rpm for the Jeep to "upshift" into the next gear. Then, I have to go almost 65mph and 4200rpm to get the Jeep to upshift again. I have to begin the whole process over again if the Jeep falls below 25mph (after reaching 35mph) and 55mph (after reaching 65mph). As you can imagine, the run-out at 35 mph and 65 mph seems like the engine is going to blow and then it finally kicks in. It makes for a miserable drive and makes driving "work" versus pleasure. I have a lot of traffic in my commute also, which makes it even worse. Also, if I punch the pedal to the floor, there is no "downshift" that kicks the Jeep into a passing gear. It just gradually gets faster with no "passing gear". The Jeep runs at 3000+rpm when I am going 65mph and it should be around 2100 rpm. I had a Mercury Cougar that had the same exact problem and it was the fan clutch (doesn't sound right, but it was). I replaced the fan clutch hoping my problem would go away, but it did not. What is my problem? It sounds like an electrical problem as sometimes it will run like a normal Jeep for a week or two, then go back to the Jeep from Hell again. The Jeep is in great shape, but I need it to perform better....or else. I have changed the TPS, fan clutch, transmission fluid, and transmission filter. Could it be the computer or the transmission computer? I could really use some expert help to diagnose this problem before I take it in to a mechanic's shop to put it under a scope. I'm a do it yourselfer and would like to fix on my own before I give in to the shop.

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post #2 of 6 Old 09-25-2007, 01:37 PM
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2000 XJ Cherokee 
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got that same issue and it wasn't my TPS either...

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post #3 of 6 Old 09-25-2007, 02:04 PM
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2000 XJ Cherokee 
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my 2000 looks like it has a mechanical downshift cable coming off the throttle body linkage.. at least the cable looks like it goes down to the tranny. maybe its broken or stuck? the tranny would think youre at wot all the time and have high shift points if thats what the cable is indeed for and its toast.

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post #4 of 6 Old 09-25-2007, 02:12 PM
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1993 XJ Cherokee 
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There is indeed a tranny kickdown cable connected to the throttle body, it is supposed to be "self adjusting" but the one on my old XJ was worn out & I had to apply a hose clamp to keep it in the correct position. Check that out first, cause it's pretty simple to fix.

There is also a TCU under your dash that might be shot? I think I have a couple of these in the garage if you're in need of one.

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post #5 of 6 Old 10-01-2007, 12:15 PM Thread Starter
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Can you identify the transmission kickdown cable next to the throttle body with a picture, please? I think I might see what you are talking about, but I do not see any way to adjust it.
If that doesn't work....I'll try anything....I'll try the TCU off of my father's 90 Cherokee to see if it works.
Did you ever get yours fixed? If so, what was the culprit?
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post #6 of 6 Old 11-20-2008, 04:10 PM Thread Starter
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2007 KJ Liberty 
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The problem was a bad TPS. The new one I put in was defective. I found this out when I purchased another one and it solved a problem I have had for several months.
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