NewJeeper13

Hi, I'm new the forum thing, so please forgive any rookie wrong-doing! I just bought an 88 XJ (4.0, AW4) a few weeks ago. The last owner was driving along about 40mph, and with no warning the tranny just feels like you put it in nuetral, and the engine dies(?!?)
It starts back up fine, but now you only have first gear, you rev it out and it won't shift into second. Then, if you let off and try to give it gas again the tranny feels like it's slipping, until you let the rpm's drop way down and you almost stop--it grabs again.
I replaced the tranny with a salvaged one, and the new tranny is doing the EXACT same thing. Surely I don't have 2 bad trannys with these symptoms .(Right?)
We checked the voltage on the tps and it checked out OK. We checked the connections from the TCU to the trans (including the inline fuse) and I am quickly running out of ideas and time to return the salvage tranny if it is the culprit. Please Help!!!!!

perez1989

Mine did the same thing and it was the TPS. $75 at autozone with a two year warranty.

Throttle Jockey

tcu controls the shift pattern with solenoids. this could be your problem. either one can cause your problem. there is a write up on how to bypass the tcu and basically shift it manually with togel switches. go to "fourwheeler.com" and search AW4. if both trannys are doing the same thing i would lean toward the tcu.

89Laredo

Disconnect the TCU and try manually shifting it. If it manually shifts fine, then its time for a new TCU. Otherwise, I would be looking at mechanical problems...

TR1Hemi

Mine was acting up, turned out I had a shorted trailer tow harness, the BACKUP light wire shorted on the frame, causing the TRANNY fuse to blow, essenitailly turning off the TCU. In short check the tranny fuse, if it blows when you put it in reverse check back up light wiring.

TR1Hemi

Check the one in the Fuse box, not the one in the harness.

98 JeepJeep

does it shift good manually?

NewJeeper13

Alright, first of all thanks for all the suggestions. I unplugged the TCU and the tranny shifted fine manually. So I guess from what I'm reading that means it's not the transmission, right? I then replaced the TCU with a salvage yard TCU (with the same colored sticker as mine.) with no luck. So then we switched out the TPS with another one that's voltage also checked good....STILL no luck! I'm wondering, do you guys think these salvage parts are killing me? Should I shell out the cash for a new TPS and/or TCU? Also if the voltage on the TPS checks out OK, does that necessarily mean it's good? Lot's of questions I know, anybody got the answers? Thanks in advance.

Metmknice

Have you checked the fuse in the box and the inline fuse to the TCU?

NewJeeper13

Yup, everything in the fuse box and the inline were good.

89Laredo

Hmm... Maybe its time to start chasing wires from the TCU. Apparently some signals arent getting sent.

Do your reverse lights work? Could be NSS related, but I dont think that woudl cause it to not shift out of first.

NewJeeper13

I still have to checkout the back up lights, but I got the TPS that was originally on it tested at Autozone, and its fine. Since I unplugged the TCU and it shifted manually fine, does that mean the tranny's OK, or could it still be one of the solenoids in there? Does shifting it manually totally skip the solenoids or do they still have to be working for it to shift?

NewJeeper13

Great news- my new 88 xj now shifts like a champ..... after the salvaged tranny swap, the TPS checked fine, The TCU swap, and checking the solenoids in the tranny..........The problem turned out to be in the wire harness between the TCU and the solenoids. While I wish I new this before spending all the money on the tranny, it's kinda hard to dwell on when it works now. + I now have quite a collection of extra parts!