AW4 TCU Source?

Hello all. Either I'm going crazy, becoming senile (I'm only mid thirtys - OK, late thirtys), or the search function here isn't working right. I searched in this forum "OEM Tech" for these key words "AW4 TCU Source", then "AW4 TCU", then "TCU", then "AW4" & got nothing. I finally just typed "jeep" to test & got several hits - of course.

It has been awhile since my last login here. But I at least expected a few hits on AW4. The XJ's Automatic transmission.

Anyway. My XJ (90, Laredo, 4X4, AW4 automatic, 307K [yesss], mostly stock).

My jeeps transmission has been acting up for awhile. I've isolated the problem to the Transmission Control Unit (TCU). I've been driving around with it unplugged for a couple of weeks doing the manual shift thing; however, I'd like to get a new TCU if I can find one cheap enough. I'm sure the stealership wants a couple of months pay for one. Anyone know of a source?

Your not going crazy... I searched NP242 sye and got nothing. Either we are doing something wrong or somethings up.

http://cgi.ebay.com/ebaymotors/JEEP...016QQitemZ260059760437QQrdZ1QQsspagenameZWD1V

Search "Cherokee Computer" on ebay motors you will find a few. This one is Buy It Now for $10+10 S&H

Im sure you have tested everything... but have you checked the Throttle position sensor? From my expirience these computers are rarely the problem.

-Tim

Ditto. The usual cause of irratic or improper shifting is a bad TPS sensor. Especially is it's still the stock one at 307k miles. What are the symptoms?

The search doesn't seem to work for me either. The email notification of new posted to subscribed threads doesn't work either.

bamaman said:

Hello all. Either I'm going crazy, becoming senile (I'm only mid thirtys - OK, late thirtys), or the search function here isn't working right. I searched in this forum "OEM Tech" for these key words "AW4 TCU Source", then "AW4 TCU", then "TCU", then "AW4" & got nothing. I finally just typed "jeep" to test & got several hits - of course.

Click to expand...

Sadly, search doesn't work for 3-letter words, as I discovered when searching for "ome", "old man emu", etc.

Sweet! Thanks Tim88XJ! I actually did a search on Ebay for a TCU before. Guess I didn't try hard enough. Thanks for the link. I've had my XJ for almost 10 years now & tested/replaced the TPS a few times (I've done the ground wire mod). My trans has been having trouble shifting between 3-4th gear (bounce between 3rd & 4th)for over a year. The problem would come & go. I also thought it was the TPS even though my MM kept saying it was fine. I even replaced it just to be sure. Problem persisted. Then I thought it was a Valve Body problem & have been thinking about rebuilding the Valve Body on the AW4 (I bought the AW4 Manual) & replacing any of the solenoids that were bad. A couple of weeks ago, the trans stopped shifting at all. It eventually caught in 1st gear, Then ran fine the rest of the way home. That made me think it must be an electronic problem (trans oil is fine). Sure enough, I've been running with the TCU unplugged for a couple of weeks & the trany shifts fine manually. If the new TCU doesn't work, I'll just keep driving it like this. Thanks for the Tips though!

fizassist said:

Sadly, search doesn't work for 3-letter words, as I discovered when searching for "ome", "old man emu", etc.

Click to expand...

Yeah it will, but you have to use an * after the three letter word.
ie, ome*.


Later

Good luck!

Also noteworthy... there is a vaccum switch that IIRC has something to do with OD and TC lockup on the brake pedel assembly. Might be worth looking into as well.

www.car-parts.com is a better bet than ebay. It will show you which TCU correctly interchanges for your year rather than having to guess, and which junkyard has one. Usually cheaper than ebay too.

The search function on this site is garbage, found that out a long time ago. Gives you everything you didn't want and nothing of what you did.

Tim88XJ said:

Good luck!

Also noteworthy... there is a vaccum switch that IIRC has something to do with OD and TC lockup on the brake pedel assembly. Might be worth looking into as well.

Click to expand...

Hey can someone explainthis to me. Which vacum switch is it? My TC has been disengaging and then kicks back in on its own.

wilson0309 said:

Hey can someone explainthis to me. Which vacum switch is it? My TC has been disengaging and then kicks back in on its own.

Click to expand...

There is a white plastic switch high up on the brake pedal that tells the TCU when the brakes have been applied. It may be gunked up and not working. As I recall, there is a single screw on the right hand side of the bracket and the bracket would slide to the right to get it off. The switch can be popped apart and cleaned. It can also be adjusted by sliding in-out if needed.

This switch also has a vacumn line going to it. When the brakes are pressed it releases the vacumn on the cruise control solenoid to help ensure that the cruise doesn't get stuck and pull an Audi.


You're issue may also be caused by a flaky TPS sensor. If you start getting erratic shifting, then definitely suspect the TPS sensor.