New AW4 Problem

I just had to go pick up my daughter due to new AW4 problem the 124,000 mile 89 XJ.

It had been rapidly shifting from 3-4-3-4-3..... at about 35 mph. That was the only issue. Then 2 weeks ago it started a rear drive shaft leak at the rear tranny seal. Fluid was slightly off (burnt orange) in color. I put in a pint of Trans-X 2 weeks ago, and the seal stopped leaking the next day. Had no problems until about 3 days ago when the rapid 3-4-3-4 shifting at 35 mph started. Figured it was just the TPS wearing out. Tonight same problem, but tended to get hung up between shifts and slip for about 1 second between the shift cycling, so I had here drive home in 3rd. By the time she got home it would not shift past 2nd gear in D or 3!

It down shifts from 2nd to first if I manually shift from 3 to 1-2 at about 30 mph. Got up to 45-50 mph in 2nd gear (shifter in 3 and / or D) and it refused to go into 3rd (no more upshift). So it has gotten suddenly worse.

Planning to test the TCU side of the TPS, check the TCU fuse and TPS/TCU grounds, and drain and change out 3 quarts in the morning using the drain plug. Will post test results when I am done.

I am hoping it is just muk in the T fluid (possibly loosened up the Trans-X).

I already tried adjusting the throttle Tranny cable twice a few days ago, but it had no effect.

TPS sounds like a likely culprit.

You can also test the TPS directly by backprobing with a paperclip.

All that shifting back and forth could have cooked some of that tranny fluid.

bigalpha said:

TPS sounds like a likely culprit.

You can also test the TPS directly by backprobing with a paperclip.

All that shifting back and forth could have cooked some of that tranny fluid.

Click to expand...

That is what I am hoping happened!! The partially cooked T fluid, and Trans X cleanup of the cooked fluid the last 2 weeks might be adding to the current problem.

Keeping my fingers crossed. Already have 3 other vehicles to work on, 2 brakes and one head job, don't need a 4th right now.

FWIW, I got my TPS at Advance Auto for around $45. I ordered it online and picked up in store same-day.

Wouldn't hurt to do another drain+fill. Remember, takes about 3-4 drain+fills (with tranny shifting in between each fill) to get all the bad fluid out. You might have some bad fluid still left.

Well I checked the TPS, both sides seem to be in good enough shape. The high resistance is a little low on both sides, but that only affects WOT outputs to the TCU and ECU, so that is not the problem. The movement is very smooth except at about 30% of WOT(an d I am not even sure it was out of spec yet). However, the shifting problem is happening at about 2-3% throttle, not at 20 to 40% throttle.

I could not get the jeep to duplicate last nights stuck in first gear problem, except when I disconnected the TCU to TPS connector, then it would hang in first gear. Both TPS grounds were extremely good, about 0.05 ohms using my good meter (not the digital)!

Only problem I could feel was the back and forth shifting (or lock-unlock-lock) at 35 mph and at about 2-3% throttle cruising speed. I am starting to think it is the torque converter locking and unlocking that I am feeling, and not a 3-4-3 shift up and down and up again. I used the 3-D-3 manual shift to verify this, and it feels very different than the problem area so I think what I fell cycling is the TC lock-unlock-lock cycling. I was able to get a slight slip, delayed 1.5 second 3-4 upshift with a slip delay after a very heavy near WOT run followed by a rapid drop off of throttle.

I drained the first 3 quarts, pretty dirty dark color, and refilled to the proper level (it was a pint too full last 2 weeks from adding TransX). Drove it for about 30 minutes after the 3 quart change, running 0-55 mph start and stop tests.

No changes after changing the fluid, but also no repeat of last nights stuck in 1 st gear problem either.

I forgot to test the TCU to TPS voltages. Will do that next time. Plan to drain and fill 3 more quarts (Dexron III/Merc, Coastal brand) via the drain plug again in a few days, at least 2 or 3 more times.

I am doing the same to my older 87 jeep, the one that has the cold morning start up with no forward until the T fluid warms up.

Anyway, I have never been sure (suspected) my 87 AW4 torque converter was locking up properly, and I am now pretty sure that the 89 I am talking about in this thread has a super sensitive lock-unlock thing going on at very light throttle when cruising at about 35 mph. If I switch from comfort to power on the TCU tranny switch, the trouble speed lock-unlock-lock thing just moves to a cruising speed of 45 mphs.

I don't think the TC should be unlocking at 35 mph steady state cruise based on my idiot light set up tests on my 87 jeep, so I am srcatching my head on this one. In fact my TC lockup solenoid power light (custom) indicator on my 87 stays lit even at TPS idle while the jeep slows down, and only cuts off at a vehicle speed of 25 mph!

Where's Lawsoncl and 8Mud when I need them?

Yeah, since the TPS seems to check out ok it seems the next thing to check is the torque converter, like you say.

Unfortunately, I don't know squat about torque converters. Good luck and keep us updated.

bigalpha said:

Yeah, since the TPS seems to check out ok it seems the next thing to check is the torque converter, like you say.

Unfortunately, I don't know squat about torque converters. Good luck and keep us updated.

Click to expand...

I don't think it is the TC's fault. I suspect something is going on with the TCU, or maybe it is normal (?) and my 4 years of experience with the other 87 jeep is abnormal?

Only other option may be a fluid pressure issue, but it gets fantastic mileage for a jeep, much better than my 87 Jeep does.

She drove it to school today. I may do another 3 quart swap tonight.