My 1990 Jeep Cherokee won't shift

The shift points are somewhat controlled by the throttle position sensor. The plug and socket on it get corroded. I clean them with a spray contact cleaner, then use some dielectric grease on the plug seal skirt which seems to last at least a couple years.

WD40 will also work as a cleaner in a pinch, but the job doesn't last long.

If cleaning doesn't help, then you can test it with a multimeter. On ohms, it will vary the resistance going up on the center wire and one side wire, and vary going opposite on the center wire and the other side wire. The resistance must be smooth.

There are voltage tests for it too. You have the engine key on run and backprobe the plug. The voltage should go from .02V to 4.8V. Same deal as above, one side goes up from .02 and the other side goes down to 0.02V and it must be a smooth transition.

Hope this helps,

Mike 86-00 CJ7 Laredo, 33x9.5 BFG Muds, 'glbutt nose to tail in '00 88 Cherokee 235 BFG AT's

davees90JEEP