aw4 tranny:constant downshifting

ok its probably been asked a million times and before anyone jumps my case, I DID SEARCH. anyway, I just bought my 95 cherokee last week. It has 160k and runs great. Unfortunatly I have started to notice an odd problem with the tranny, as of yesterday. What it does is its seems to get 'confused' or wants to downshift...all the time. Sometimes when Im cruising around at 1/4 to 1/2 throttle it acts like it forgets whats going on and either doesnt shift and kind of jerks or it searches. also, I notice that recently as soon as I tap the throttle to accelerate, no matter how little throttle I give it and no matter what gear, it will downshift. Its almost as if it cannot accelerate in the gear its in, so it shifts down. I suspect the TPS, but I have owned numerous cherokees and have never had a problem like this. I know the aw4's are near bulletproof so I suspect an electrical problem. Im just wondering if this sounds like a common issue with the TPS. If not, would anyone have any ideas...id hate to think I just got screwed on this jeep! thanks!
PS if it helps, I powerwashed the engine bay and began noticing problems, soon after!

My 96 has always seemed to downshift early, like around 70-80 MPH if I give it a bit too much pedal. Other gears also but not as noticeable.
Sounds like the TPS may be acting up. I've also read about a relearn process for the ECM, that is supposed to affect this also (it's in the troublehsooting list).
It's also possible the TV cable is out of adjustment, but this usually affects downshifts at near full throttle or above 3/4 throttle.

yes its very strange. Like I mentioned I have owned I think 3 cherokees now, all with the aw4 and this is a first for me. what Im saying is not that it shifts too early, because from 1-2, 2-3 and 3-4 under steady throttle it shifts fine and on time...BUT, for example if I was in 3rd gear and gave it 1/4 throttle (or less) just to scoot a little faster, it would shift into 2nd immediatly, instead of just moving a little faster in 3rd gear...its just like it cannot accelerate without the downshift.

If it's had an exhaust header changed or the TB removed at any time, it's possible the TV adjustment is out. The TV (among other things) is passing gear.
If the TPS was acting up, it seems likely it would affect engine performance also.
My 96 downshifts earlier or with less pedal than my 2 Renix's have. But usually around 3/4 pedal or so. It gets irritating sometimes, you have plenty of power and torque left, but the motor (ECM) insists on downshifting anyway.

yeah I havent had the jeep long but I know it was owned by an older gentleman (one owner) before me. Its just annoying me becasue I know this isnt the way its supposed to work, as it worked fine until I washed the engine bay. I wish it didnt get dark so early so I could check it out. Does anyone know the correct way to check the volatge on the tps of a non-renix cherokee?

OK I went out and tested the voltage and according to my fluke, its putting out 10.56 volts on the input side, and 10.67 volts on the output side. When I divide the output volatge by the input voltage I get a ratio of 1.01. I think this is waaay out of range, someone correct me if Im worng. Im just curious if this was so far out of true, how come the jeep doesnt run like crap and or trip a code?

> as it worked fine until I washed the engine bay.

There's your problem!

A few years ago my Jeep was fine until I washed the engine and afterwards shifted the same as yours.

At that time I didn't have this forum to help me out so I had a local garage look at it. At first they recommended to rebuild the tranny...but then I told them it was fine until I washed the engine. I don't remember what they replaced but it was either the TPS or CPS. Only charged me $125.00. Better than $1600.00!

I learned my lesson...no water near the sensors or engine.

8Mud said:

My 96 has always seemed to downshift early, like around 70-80 MPH if I give it a bit too much pedal. Other gears also but not as noticeable.
Sounds like the TPS may be acting up. I've also read about a relearn process for the ECM, that is supposed to affect this also (it's in the troublehsooting list).
It's also possible the TV cable is out of adjustment, but this usually affects downshifts at near full throttle or above 3/4 throttle.

Click to expand...

The tranny cable controls the internal hydraulic pressure in the tranny, which only affects shift firmness. Shifting is controlled entirely by a seperate trans computer, not the ECM. Shifting is based on the TPS input (ie how much throttle is being applied) and the output shaft speed (sensor on rear drivers side of the tranny. There is a switch on the brake to help decide when to lockup the torque converter. AW4s after 1996/1997 have an additional input shaft sensor.

A bad TPS will cause the trans computer to think you are applying more or less throttle and cause these symptoms. I would start by checking this with a meter. Do a search on TPS and you'll find more info.