Jeep AW4 Transmission Problem

[Xernicus]

Wondering if anyone can give me some pointers/advice on what's going on here.
I've got a 97 Jeep Cherokee 4.0 that I use as my daily driver. It's always ran and drove great, but last week the thermostat stuck shut, and cracked the radiator.
(The CEL came on a week before this happened pulling a "Shift solenoid B" code, but my local transmission shop said it looked fine. Cleared the code and it hadn't come back on in 750+ miles)

Replaced the tstat, radiator, and hoses and went to take it on a test drive. Other than idling rough, it drove and shifted fine. Got back home and ran a compression test, and found out that the piston rings expanded and seized the piston when it overheated. I partially rebuilt the engine and got it back together the other night and took it on a test drive.

From my driveway, everything seemed great until I came to a stop sign down the street. I probably cycled through 1 though 3rd gears, not going into OD, but it drove fine.
Tried to accelerate from the stop sign and it felt like the transmission was *seriously* slipping. Cycled the shifter from park back into D4, problem continued. Put it into reverse, and sure enough it had power. As a test, I locked the transmission into 1-2, and it went forward no problem. Manually shifted into 3rd, and finally D4 and it still kept driving great. Once moving, it down and up-shifted perfectly fine. No issues going up hills, and the torque converter seemed to lock-up just fine at speed.

 

So I got back home, wriggled some wires around, played with the transfer case shifter, and tried a test drive again. Transmission worked perfectly fine, this time it had no issues with downshifting or engaging when I came to a stop. Drove it back and forth to work yesterday, worked fine as usual. Today, I was going to go on a roadtrip, and sure enough... transmission started slipping again at the exact same stop sign. Once again, it drives fine if I manually shift down to 1-2 to accelerate from a stop and manually shift it up to D4.


I'm thinking something got f-cked up when I was doing the piston job. The one thing that rings a bell is that I had to lift the transmission a few inches so I could pull the oil pan off without it running into the axle. What's the likelihood that a screw going through the chassis "bit" one or a few of the wires in the harness located above the trans or disconnecting the linkage when I lifted it?

I did confirm there's an issue with the "B" Shift Solenoid or the wiring to it; it measures 280ohms of resistance, compared to 13.5 for Solenoids A&C.

From what I've read, a faulty shift solenoid can give these symptoms, but I find it very weird that the thing drives great from a cold start until I come to a stop, and the problem has been intermittent at best. The fluid and filter is pretty much brand new (only ~750mi on it), and perfectly topped off. Nice cherry red/pink, smells fine.

 

I suppose what worries me the most is that my research has also pointed me in the direction of the front clutch having overheated and giving up the ghost. But this also doesn't make sense, because it drove and shifted just fine after I replaced the tstat and radiator (before I pulled the head and pan off).

*sigh*... I'm simply at a loss for what's wrong with this thing. I could take it into the same transmission shop, and get a discount on service since the original problem (CEL) replicated itself... but if this is likely something simple I want to save my money.

 

My OBD II reader pulls the following codes:

P0700 - Transmission Control System (afaik this means there's a code stored in the TCM, not that the computer failed)

P0758 - Shift Solenoid B - Electrical

 

Any advice is much appreciated.

[Xernicus]

Got this sorted out. OBD codes were correct that the shift solenoid failed. Read from 266- 600+ ohms of resistance when testing it directly. There are no wiring problems (thank god, since I paid $750 for a new wiring harness + install just a few years ago)

Transmission computer was not initially dead, but it soon failed with complete communication failure (No bus).
Oddly enough, after replacing the solenoid the transmission shifted fine despite the computer being faulty (per DRB-III diagnosis). It did feel a little funny though, I think it was still in "limp" mode and the torque converter was still unlocked.

 

TL;DR: FIXED. Faulty TCM, Shift solenoid, dirty grounds. Wiring, front seal, clutches+band pack, and flexplate all OK.
Off-topic: Replacing failed catalytic converter so I can pass emissions next year.

Total cost: ~$500 (with engine rebuild, and cooling system ~$1k)

Current mileage 238,000 miles.

Edited August 11, 2017 by Xernicus

[Aft3rmath]

Glad to hear you got it figured out!  Didn't realize there were fellow Jeepers here!