88 XJ trans issue

I just bought a 88 xj 4.0L AW4 Np231 runs good trans wont shift its acting as if the tcu is disconnected. If I manually shift it from 1 to 3 to D on the shifter it shifts pretty good. but if I just put it in D its like its in 3 or OD and wont shift. checked the fuse it was good and has power to it when the ign is on. any ideas where to look? I searched for Tcu threads and couldnt find anything. feel free to link me a thread with the info I might need.

If the fuse is good (the one in the TCU harness behind/under the glove box) and none of the pins have backed out of the TCU connector, I'd check the ground. Ohm check the ground (black wire) from the TCU to the ground on the dipstick holder/brace on your motor. Where the wire went into the crimp on the ground ring on mine was really corroded. I cut it off, stripped a new section of wore and soldered a new ring on there.

There is also a resistor wired into the harness near the TCU fuse behind (under) the glove box. I've found the resistor loose before and re soldered it, though to tell you the truth I don't really know what the resistor does or why it's there.

There is also a fuse in the main fuse block under the drivers side dash. It is marked TRANS.

B.RAIDER said:

There is also a fuse in the main fuse block under the drivers side dash. It is marked TRANS.

Click to expand...

That's for the Power/Comfort switch and I believe reverse lights only.

Main power for the tCU is in the yellow taped harness up under the kneebar/glovebox.

Unplug both connectors near the trans dipstick tube and have a gander inside. Perhaps spray them out with a good electrical cleaner and look for retracted or bent pins. There's a black set and a gray set. Easy to spot.

Thanks Im gonna check the tcu fuse. I didnt know there was another fuse. I only checked the trans one in the main fuse block under drivers side dash.

Well neither fuses worked. next is checking the grounds. then if that dont work possibly a new TCU

See post 4. Did you check the connectors as advised?

well checked those connecters all was clean and good but still same problem. also wierd thing if I turn headlights on without the key and shut them off they stay on. but as soon as I turn the key forward they go off. what could cause this? or is it some sort of mod or something? it does it everytime.

not to jack your post but my jeep is doing the same exact thing. Even with he headlights deal also.My thread is at the end of the page. If you find something please let me know i have seem to have checked everything on mine. no luck....

XJeeper87 said:

well checked those connecters all was clean and good but still same problem. also wierd thing if I turn headlights on without the key and shut them off they stay on. but as soon as I turn the key forward they go off. what could cause this? or is it some sort of mod or something? it does it everytime.

Click to expand...

The head light deal is OEM stock, they all do that. So it is not the Droid you are looking for, LOL.

Next step IMHO is to drop the pan, and check each of the three electric solenoid valves. One of them, #1 IIRC, causes your exact symptoms when it goes bad, or looses the wiring feed to it. They can be tested with a 9V battery. I took mine out, and just checked to see if they sealed, and opened (blow on one end) while connecting the 9V battery and disconnecting it. While in there check that one of the solenoid wires is a good ground to the battery negative post!!!