Trans Problem; FAQ I know but haven't found an answer yet

First things first I have an 89 XJ 4.0L AW-4 transmission with 96k on it.

Problem is when I accelerate the transmission seams to shift to early leaving it with little power to accelerate. After I have reached speed I the transmission wanders in and out of over-drive as I try to maintain speed. I've seen a lot of posts about transmission problems but everyone seams to be having problems with slippage, I don't get any slippage just random shifting. Also it doesn't want to down shift if I get on the gas.

I've seen post suggesting problems w/TPS causing transmission issues. I haven't checked this yet but plan to do so. Any other suggestions would be appreciated.

The TV cable is another thing that if improperly adjusted will cause just the symtomes you describing. To properly set it to factory specs (moter off) push the little tab down on the bracket, open the throttle all the way, then release the button, then the throttle linkage. Go fro a test drive to check it all out.

scoobyxj said:

The TV cable is another thing that if improperly adjusted will cause just the symtomes you describing. To properly set it to factory specs (moter off) push the little tab down on the bracket, open the throttle all the way, then release the button, then the throttle linkage. Go fro a test drive to check it all out.

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Actually the throttle cable shouldn't affect the shift points on the AW4. It only controls the hydrualic pressure and affects shift firmness. The tranny computer controls the shifting based on the TPS sensor input and the rear speed sensor on the tranny. I'm voting for a mis-adjusted or bad TPS sensor. A bad rear speed sensor would cause it to not upshift or upshift very late. If you have a meter, google for the TPS adjustment procedure, and try adjusting the TPS. Also make sure the resistance changes smoothly and isn't jumpy (dirty or bad tps).

I tested the TPS (i've seen that be the problem on many other threads) but it looked within specs so i adjusted it and i am still having the problem. Do you think it could be possible that the TPS would test well but still be causing the problem. I have also seen some suggestions for the transmission soleniods.

lawsoncl said:

Actually the throttle cable shouldn't affect the shift points on the AW4. It only controls the hydrualic pressure and affects shift firmness. The tranny computer controls the shifting based on the TPS sensor input and the rear speed sensor on the tranny. I'm voting for a mis-adjusted or bad TPS sensor. A bad rear speed sensor would cause it to not upshift or upshift very late. If you have a meter, google for the TPS adjustment procedure, and try adjusting the TPS. Also make sure the resistance changes smoothly and isn't jumpy (dirty or bad tps).

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I would still recommend making sure the TV is adjusted properly. I experimented with it once due to a hunting issue at about 30-32mph(3-4 upshift). If I gave the TV one click of preload, it would stay in third until about 35mph. I didn't go any farther than one click though. My two cents.

PaulSunset said:

I tested the TPS (i've seen that be the problem on many other threads) but it looked within specs so i adjusted it and i am still having the problem. Do you think it could be possible that the TPS would test well but still be causing the problem. I have also seen some suggestions for the transmission soleniods.

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Did you check both sets of wires coming out of the TPS? Did the voltage vary as expected when you moved the throttle through it's range? One set goes to the engine computer and the other set goes to the Trans Computer. Your symptoms really do sound like a TPS issue.

A bad solenoid would cause it not shift properly, for example skipping gears (ie jump from 1st to third) or fail to engage the lockup. If you are having a problem where it is failing to shift into a particular gear, you can test for a bad computer controlled solenoid. Pull the trans computer fuse and make sure the transmission shifts into gears properly with the shifter - this will help confirm that it's not a mechanical problem. In fact, it's the first test listed in the fact service manual. The fuse is on the wiring harness next to the computer under the passenger side of the dash.

I've seen a dirty switch at the brake pedal cause the torque converter to fail to lockup. It's signals the trans computer to unlock the converter if you apply the brakes. You can check that out at highway speeds. Without changing throttle position, tap the brake with your left foot and you should see the converter unlock and the rpm will jump a few hundred rpm.

Same thing happened to my '87. Unplugged the square TPS connector of the two, sprayed cleaner into both sides, and on the TPS side plug took a small screwdriver and closed the terminals slightly for a better connection. Kind of a crude repair but it worked! Shifts timed correctly and got my kickdown back.