1988 xj Transmission?

My 88 auto transmission seems to drop in and out of overdrive on the freeway. I do have over 200k on drivetrain. Any ideas are appreciated.

How often do you change the ATF in the transmission? The owner's manuals says 15,000 "severe" and 30,000 "normal".

My dealer has a machine to change out the fluid but unlike the Jiffy Lube type places they first put in a can of cleaner made my BG Products. Then they let the transmission warm up to operating temperature. Once the transmission is to temperature then the do the transfusion.

I have had several coworkers say it did a great job on their vehicle. I also did it on my 88 XJ and it made a difference but I was flushing out synthetic Mobil 1 ATF. The Mobil 1 allowed too much slip and I lost 3 mpg.

I think the easiest place to start is the transfusion, with 200K on the transmission there may be some stuff in the oil causing the problem and a 100% change out is the only ticket to get rid of it.

Also there was a TSB sent out by Jeep saying to make sure the ATF bottle has a Dextron Certification number on it. The Number will begin with a "D".

Your throttle position sensor may be failing. Have you ever changed the TPS?

Erik
88 Comanche

I have replaced the TPS about 10K miles ago. I also change my tranny fluid every 15k, but I have not done a full transfusion. I'll give it a try

AW-4's shifting is computer controlled. Sounds like a computer/sensor problem to me. Mine shifted perfectly all the way up to the very grinding, metal shavings, and bitter end at 169k. It even drove itself to the tranny shop shifting perfectly, just grinding all the way too.

Definitely follow up on the transmission fluid transfusion, but you should still check the electrical values of the TPS. I discovered to my financial horror that I killed my replacement TPS when I sprayed it with water as I was cleaning my engine. At the time, I couldn't figure out why my transmision was acting up inasmuch as I had replaced the TPS only a year earlier. As it turns out, the TPS is verrrry intolerant of water.

Erik
88 Comanche

Eric I concur on the TPS being overly sensitive to water

Check your brakelight switch. when the brakes are applied the switch tell the Tranny computer to unlock the converter (to make it live longer).
I have some rubbed through insulation on the wiring harness that caused the switch to ground out when I went over the larger potholes. Thereby caused the revs to comeup about 500 rpm.

$0.05 worth of electrical tape saved me a trip to the transmission shop.

i have to echo eric here.... TPS + H2O = bad ju-ju. mine still isnt backto normal after 2 weeks..
mike

Thanks for all the input guys. You're the greatest. It's funny, this problem is intermittent. This morning coming in to work, it was fine, no slipping in and out of overdrive.

Bought an XJ for a handfull of dirt cuz some guy sprayed his intake / TB with a power washer and couldnt figure out why the AW4 shifted funny.... =)

On the other hand....had one XJ's engine completely under water for 45 minutes.....TPS lasted another 50,000 miles with perfect function. Go figure.