89 cherokee transmission problem

[bman68]

I have a 89 cherokee laredo the auto transmission seems to slip when crusing at a steady speed, rpm goes up and down and it seems like it shifting all the time its not a chunky shift, I changed the fluid and now it seems worst is the tranny shot or is it something else

[89ltd]

any problems with your speedometer? A bad speed sensor will make it go a bit crazy.

[bman68]

speedometer is ok it downshifts from 4th to 3rd holds it in 3rd for adout 6 seconds shifts back to 4th speed stays the same

[oneav8or]

I am having the same issue, and it only is getting worse not better. It seems like a sensor issue, something electrical and not mechanical, like something is telling it to shift for no reason, then shifting back.

Today it got real bad. While going about 55 MPH, it was like the transmission just went bad and I was in nuetral. I coasted to a stop and tried again. It would move, but only in 1st gear and when it would normally shift (about 15 mph under normal load) it went freewheel again like it was in nuetral. Once I slowed again, 1st gear would engage and I could move. I went about a mile till I could pull off the road, and turned the jeep off and called for help. I decided I would try to meet them halfway or as close to home as I could get at 15 mph. But now the Jeep would shift almost normal aside from the complaint above that it's been doing the last few months. Anybody have an idea what's going on?

1988 Jeep Cherokee Laredo 4.0L 6 Cyl. 289,234 miles Automatic Tranny

[Saudade]

What speed does this occur at Bman?

What happens if you select 3 or 1-2 with the shifter?

[StvDiego]

I have an '88 with the same engine/tranny and had the same problems when I bought it, changed the TPS (Throttle Position Sensor) and have had no shifting probs for over a year. Might try cleaning the connector near the throttle body, check the voltage of the unit and be sure it's adjusted properly. oh, and do a search here for TPS or tranny probs, lots of info...

[oneav8or]

Thanks StvDiego, hopefully this will help us. Will post back with results.

[oneav8or]

StvDiego, the TPS was out of adjustment. Checked the voltages and they were off, because the set screws (2) were loose and allowed the TPS to rotate. Seems to have fixed it, no sign of the strange shifting problems. Thanks for the suggestion

[bman68]

happens at every speed on 3rd in 1-2 it seems to stay in firstgear hen cruising i barely touch the gas peddle and it shifts down rpms go up will check the tps this weekend

[JeepTrouble]

My 1990 jeep had that same problem, it would try to shift but it just couldn't make it. It was an exterior transmission sensor, the part costs like sixty bucks and is actually really common in older jeeps.....

[raeuspius]

Replace Throttle Position Sensor. This not only coordinates the mixture of air and fuel but also sends a constant but varialbl signal to the Transmission to tell when to shift. There is also a cable that moves the same distance as your throttle cable. That is the mechanical end though.

This VERY common mis diagnosed "BAD TRANNY" is because the TPS dictated operation of servo engines and the electronic part of your transmission. It gets confused and will not "slip" but simply come out of gear. This is the very last symptom. Before this happened, I would bet any thing that your XJ bucked when at a cruizing speed and on a coasting speed. You had to either push the gas to stop the bucking and then break because you eventually get going too fast... lol

Don't waiste your time with a used TPS!. Pay the 60-95.00 for a new one.