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transmission issues?????

blazinjames

NAXJA Forum User
i have a 89 jeep cherokee, 4x4 auto aw4 with np242.

my transmission seems to be going. in the last week or so ive noticed it shifting late, it seems to rev up too high before it changes gear. normally it will shift around 3000rpm but today i brought it up to 5000 with out it changing gear so i stoped to check the fluid, level looked a bit high actually

can i fix this or should i look into replacing the transmission??
 
The AW4 tranny is electronically controlled, and the shifting is controlled by the transmission computer based on speed and throttle position. If it's shifting too high or too low, it's usually not a mechanical problem. The AW4 is actually pretty robust mechanically. More than likely your problem is a bad Throttle Position Sensor (TPS). It's located on the throttle body and they do eventually wear out and cause shifting problems.

The TPS sensor can be tested with a voltmeter, preferrably an analog one that can show if its changing smoothly without any bad spots. A good analogy for the sensor is like an old style volume control and you're probably familiar with how those can get scratchy and have bad spots. I think a new one is around $30-$40?

The throttle body to tranny cable (sometimes incorrectly called a kickdown cable) affects the internal hydraulic pressure and hence shift firmness. It does not control when to shift.
 
oh ok..im going to test the tps tomorrow and see about checking the cable

how exactly do i check it with voltmeter? with it running, do i need to give gas or shift at the same time?

is the tps sensor under the hood?
 
Get a hold of a good manual for this type of testing. I'd suggest the factory service manual but Haynes and Chiltons as a backup plan, as I believe they would have these procedures in them as well.
 
oh ok..im going to test the tps tomorrow and see about checking the cable

how exactly do i check it with voltmeter? with it running, do i need to give gas or shift at the same time?

is the tps sensor under the hood?


tps is on the front right side of the throttle body. 87-90 tps is also adjustable and needs to be set up to spec. even if you replace the tps with a new one, it still needs to be adjusted to spec.

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm
 
There is also a transmission cable adjuster right behind the throttle body. The transmission cable slides through a sleeve with a button on the top. If you depress the button, you can slide the cable sheath, extending or shortening the cable, and this does affect the shifting delay. I would only slide it an inch at a time one direction or the other, and then test drive it to see if it is an improvement. If no improvement is noticed, you can return the cable to the original position.
 
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