AW4 slips in and out of overdrive

[fspell220]

It's a 89 cherokee w/4.0. This only happens anywhere from 45 mph and up. It happens alot more when I'm running about 65 (highway speeds). I've noticed that it will quit slipping if I slightly let off of the gas. It seems to do it only when I'm above 45 mph and when I'm apply the gas pedel. Here is a list of things I have already done (way prior to it acting up)
-change fluid and filter (dextron 3) about 10,000 mi ago. fluid still looks and smells fine.
-adjusted tv cable

Any suggestions would greatly be appreciated. Thanks
:wow:

 

[anodyne33]

Stock tire size?

 

[ZacSquatch]

Mines been doing this with 2 differnet transmissions in the same jeep... First time it was a crapped out and broken torque convertor. Still dunno wahts up this time.

 

[fspell220]

sorry, yes the tires are stock, everything is,and mileage is 205,000

 

[clunk]

the TPS can really make the tranny act up in just about every situation.

 

[BIGSLVRXJ]

My 99 XJ does this in the morning when it's cold. I'd be interested to know what it is.

 

[lawsoncl]

Is it shifting into third, or maybe the torque converter is unlocking? The torque converter unlocking at speed will let the rpms drift up a few hundred. First thing to check would be the TPS sensor as they do wear out and the trans computer uses that signal to help determine shift points and when to lockup the torque converter. It's a very common problem, especially if for the older Jeeps that still have the original sensor. Figure $35-40 for a new sensor at the auto store. If you replace it do a search for the instructions on adjusting it afterward (although you'd probably be pretty dang close just lining it up with the dirt outline from the old one).

 

[fspell220]

I appreciate the advice. It almost seems that it could be my torque converter unlocking. Yes it is shifting into third. It shifts perfectly up until I reach 4th and the above mentioned speeds. But I will try to test my tps w/ a anolog meter and see how smooth the transition is. If it checks out fine, what would be some other things to check?

 

[lawsoncl]

I'm betting on the TPS myself. If it's dropping in/out of lockup then another possibility is that the brake sensor for the tranny computer might be gunked up or out of adjustment. On the Renix Jeeps, it's a switch switch way up near the top of the brake pedal arm. It can be removed, carefully popped open and cleaned.

If you have a meter you might also check the solenoids by measuring their resistance as the trans computer connector. As I recall the nominal resistance is 11-15 ohms. Measure between pin C14, C15, and C16 and a chassis ground. C16 is the lockup solenoid. I doubt the S1 and S2 solenoids are bad because they should both be off in 4th gear.

Also have a look at the ground strap between the engine and the firewall and see if it's not falling apart or badly corroded. It's a braided strap that comes off the back of the head on the drivers side. It's probably not the problem either, but it is a common problem on the older Jeeps and causes lots of wierd problems too.

 

[fspell220]

Those are alot of awsome things to check. I really appreciate all of the help. I will check all of the above mentioned tomorrow sometime (maybe all except the solenoid check as I'm not to sure if I'm electrically savy enough to perform the test correctly-but I will try to research it and figure it out). I have also heard of the faulty ground strap problem on these renix xjs. That will probably be one of the first tests I make. I will follow up with my results. Thanks.

 

[8Mud]

Is it bucking or slipping? Does it kind of do the thunk, thunk, thunk thing or is it actual slippage.

 

[fspell220]

No, it's not slipping or bucking. It just falls out of 4th into third over and over again when I'm going over 45 mph and up

 

[8Mud]

No, it's not slipping or bucking. It just falls out of 4th into third over and over again when I'm going over 45 mph and up

Kind of like passing gear? You mentioned when you change the pedal position it stops, correct? Can you near full pedal and kind of accelerate through it. What is your top RPM, when driving?
Reason I'm asking is, a bad O2 sensor will lean the motor out under certain circumstances and fool you. Fooled me. I sure thought it was downshifting and up shifting, kind of stuck in a up shift down shift cycle. Or maybe a torque converter lock up cycle, in and out, in and out.
I finally noticed most of my trouble was right around 2000 RPM and low vacuum, throttle opened above half or so. And again in the upper RPM range, I really didn't get much out of the motor above 3500 RPM or so.
Just a hunch.

 

[clunk]

Have you tried unplugging the TCU? You should be able to check the mechanical soundness of your transmission by unplugging the fuse under the passenger side dash (on my 1990 it's a couple of yellow wires with a fuse). If you unplug it, you should be able to shift the transmission like a standard, except the torque convertor won't ever engage. You should be in the following gears after you unplug the TCU:
1/2=1st gear only
3=3rd gear only
4=4th gear only
r=reverse
n=neutral

You can drive around in "limp mode" with this fuse unplugged, just expect a slight mileage drop as the torque convertor won't be locking up and be very careful to manualy shift at the right times. eg, start in 1/2, rev it a bit higher than normal then shift to 3. Basically, you wont have 2nd gear. Make sure to not start from a stop in 4th gear as it'll create alot of extra friction and heat.

I'm still betting that you are having TPS problems, though..not actual transmission problems. Try checking the connection at the TPS harness first, then try adjusting the TPS as it may just be slightly out of adjustment. If neither is the case and the TPS is still suspect, it's time to replace. The TPS sensor for Renix era jeeps is more expensive than on the 91+ jeeps, I think mine was around $110. Try going to a junkyard first--I picked up a handfull of random sensors for $20 once, although unfortunately the jeep had already been stripped of it's TPS.

 

[UNCC_99XJ]

Another vote for looking at the TPS. Mine did this about a year ago...i'd be running down the highway with no problems when all of a sudden it would pop out of OD....shift between the two for a few seconds, then straighten itself out again. New TPS did the trick.

 

[fspell220]

Here's an update. I think it is the switch at the top of the brake pedal that controls the torque converter, because I can replicate the behavior of the jeep exactly by keeping a steady foot on the gas and pressing the break at the same time. It's definetly unlocking, so what do you think? Think it's the switch getting stuck sometimes? I've got my money on that. But I would like to know if anyone knows of a way to check/adjust/clean this switch. Or maybe if anyone knows what it's called exactly and where I could get one. Thanks in advance.

 

[lawsoncl]

It's not too hard to remove the switch and clean it. You just have to be part contortionist to get to it. :} The metal bracket that holds the switch has a screw on the right side, facing the passenger side. I think it had a 1/4" hex hex, but I'm not real sure. You'll probably have to find it by feel but it's right behind the stamped M in the bracket on mine. If you take out that screw the bracket will slide to the right and come off. That's easier than trying to unscrew the switch from the bracket and having to get it back in the same place. The switch itself can be popped apart by carefully pressing in the little tabs on the side. Here's what the switch looks like (part of the bracket is missing).

 

[Shorty]

if you can replicate it with the brake pedal, I'd say the switch is prolly functioning as designed-- it's unlocking the converter when you move the brake pedal. I would definitely look toward the TPS for your culprit-- a flat spot where you have driven it for 205000 miles isn't too hard to believe!

 

[90Blue_XJ]

Another vote for TPS. Mine did the same thing on my move from Georgia to Texas and I thought it was the tranny going bad. AAMCO put their scanner on it and it showed that the torque converter was unlocking at the OD setting but everything else was perfect. Read up on the problem on this forum and then replaced the TPS and adjusted it. No problems with it afterwards. Now has over 250,000 miles on it and strong as an Ox.

 

[fspell220]

Ok, I have a chance to work on this tonight. I tried searching but couldn't find anything. Can someone tell me how to test the tps with an analoge volt meter. Like what should it read with the throttle closed and wide open, and which wire to even hook the leads up to. I will also remove the switch on the brake pedel and look at it too. Thanks for the replys.