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AW-4 stuck in first gear

W

WTF

NAXJA Forum User
Location
Raleigh, NC
After searching, I have come here. I am working on an 87 XJ that has an AW4 that will not shift out of first gear... i feel like i recall this being a symptom of the TCU being dead. Does anyone else know what could be causing the tranny to be in 1st gear and never lock up?
 
WTF said:
After searching, I have come here. I am working on an 87 XJ that has an AW4 that will not shift out of first gear... i feel like i recall this being a symptom of the TCU being dead. Does anyone else know what could be causing the tranny to be in 1st gear and never lock up?
Click to expand...
What do you mean by "lock up"? The AW-4 will not lock the Torque Converter up in first gear. Only second through fourth.

As for being locked in first gear. If the TCU dies they will go into a fail safe mode where they will stay in any gear you put the shifter in.
 
It is the TCU and if you have the balls to try it you can rev it out to 5000rpm and it will shift but not until it reaches the screaming point. It will rev like this everytime so get used to drag racing.

You can get used TCU's at the junkyard for around $50 and a TPS is also a good idea.
 
Does it shift into 3rd if you move the lever?

If so, you might check the fuse for the TCU. TCU is a pretty hardy unit, so unless it just completely fried then it's likely going to be your fuse. :) Ran into this once myself many moons ago with mine. :D
 
Mine did that and it was the TPS, if you unplug the TCU, see if you can manually shift it into different gears.
 
Just to clarify. If the TCU does not have power, you should get 1st gear in (1), 3rd gear in (3), and 4th in (D) and no converter locking. This is actually how the FSM recommends checking that the transmission is okay before looking at any of the electronics.

Before you replace the TCU, do some basic checks. Check the TPS sensor as that can cause it to not upshift. Pull the connector off the TCU and check the resistance on the solenoids which will tell you if one of them is bad. With everything hooked up, you can verify that the TCU is applying power to the solenoids (ie telling the trans to shift). Put the xfer case in neutral and the tranny in gear and check that you are getting a signal from the rear output shaft speed sensor. On an 87 it's a magnetic switch that closes once per revolution. If that speed sensor is dead, the tranny won't know you're moving (on a 96 or later this will throw a code).

If you still think it's the TCU, I have an extra from a 1990 that I'll be happy to mail you for $25. I'm pretty sure it will work.
 
thanks for all the replies so far. just to clarify, the tranny sticks in first gear whether in 'D', '3', or '1' . The truck also has no tach but i'm pretty sure i was no where near redline when I drove it up the street and back so no test for that.

I've got a spare TPS that i'll try when i get to it. I just threw away 2 spare TCU's from parted out rigs in the last 3 months :rolleyes:

I plan to check the TPS connections, and if that's a no-go, then attempt to unplug the TCU, and check the results.

I'll post results and possibly be contacting the person with that spare TCU this weekend. I'm in NC for the week and the jeep is in atlanta.
 
Got back down south today,

Unplugged the TCU and drove her home tonight with 3 gear selections.

Tomorrow i'll F with the TPS.
 
Replaced the TPS this morning, and everything is functioning properly.


now on to the couple of other little projects.
 
Un-Plug the TCU and see if it works manualy, if it don't, if you still only have 1st the problem in not anything electrical. Not the TCU not the TPS.
 
Blaine B. said:
Someone should sticky this, as a FAQ teaching people what NOT to throw away........:rtm:
Click to expand...

No space to keep all the crap...

Anyhow, it turned out that I didn't need a spare TCU anyways, but did need the throttle position sensor which I did keep.
 
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