Tranny Issues

Forgive me if this is a repeat. I searched and found nothing. I Have a 1990 XJ Loredo. 4.0 with the AW4. I went wheelin a while back and the jeep worked great. Drove it all the way home from barstow to Palm springs. Again worked fine. Hopped in and was gonna go wheelin again and the tranny no longer shifts. (Starts in 4th). I said "shit, gonna have to replace the tranny". I replaced the tranny. Same problem. Replaced the throttle position sensor, same problem. Been through 3 tranny computers. Tranny shifts fine when the computer is unplugged and I shift it manually. I'm at a loss. ??? Any help would be appreciated.

As you've discovered, the tranny is fine. Sounds like no power to the tranny computer to me. Time to start checking out the wiring and tranny fuse. http://www.transonline.com/transdigest/magazines/1997-10/Shift Pointers/index.html

Thanks for the help. Failed on voltage for 1-2 and D. Think it may be a Nuetral saftey switch. What do you think?

Crawlin_XJ said:

Thanks for the help. Failed on voltage for 1-2 and D. Think it may be a Nuetral saftey switch. What do you think?

Click to expand...

Yeah, those are the signals from the Neutral Safety Switch. Power to the NSS and reverse lights comes through the transmission fuse in the fuse box on the drivers side. Not having those signals should not cause you to start out in 4th though.

There is a fuse taped up in the in the harness near the connector for the trans computer that feeds the +12volts to pin D16 on the connector. I was thinking maybe that was blown or the wires damaged. Your symptoms sound like a problem with power to the trans computer which will cause starting out in 4th.

Is the wiring from the trans computer, through the firewall and doen to the tranny in good shape?

Looks ok. I have power to the computer and both fuses are good.

With the key on and the trans computer plugged in, you should have voltage on pin C16. That is the output for solenoid #1 which should be activated to get 1st gear. Solenoid #2 and #3 (t/c lockup) should not have voltage to them for 1st gear. No power to either #1 or #2 is what gives you 4th gear.

So if you don't have power to just Solenoid 1, and you have good power to the TCU, then normally its either a shorted solenoid or a bad TCU. But you've replaced both of those already...