crazy overdrive

[tubsc66]

Hello, I bought a 94 Grand Cherokee Limited about a month ago and
in the past 2 weeks its developed some odd behavior from the transmission. When I reach 50 mph on the highway the transmission
drops into OD like it should but when the speed gets to 65 mph,
it drops back into 3rd gear. This happens when Im just starting out,
and the problem goes away after Ive driven it awhile. The previous
owner said the tranny was rebuilt 8 months ago, it did not exhibit
this behavior till about a week after I bought it... I have had the
transmission flushed but the problem is the same. Any thoughts?

[msrjeep]

i would have the TCM reprogrammed.

[xj31]

is it a 4.0 or 5.2?if its a 4.0, it has a tcm but it cant be reprogrammed.5.2 doesnt even have a tcm.the simplest thing is to make sure the throttle valve cable is adjusted properly

[ShadMan]

Originally Posted by tubsc66

Hello, I bought a 94 Grand Cherokee Limited about a month ago and
in the past 2 weeks its developed some odd behavior from the transmission. When I reach 50 mph on the highway the transmission
drops into OD like it should but when the speed gets to 65 mph,
it drops back into 3rd gear. This happens when Im just starting out,
and the problem goes away after Ive driven it awhile. The previous
owner said the tranny was rebuilt 8 months ago, it did not exhibit
this behavior till about a week after I bought it... I have had the
transmission flushed but the problem is the same. Any thoughts?

Hi, I'm new to this forum!

I am having this exact same problem with my wife's '94 JGC Laredo, 4.0L 6-cyl 4x4. At around 57mph it downshifts from OD, then upshifts again at about 63mph. It also downshifts when slowing down when it hits 57mph, then upshifts again to OD around 53mph. Something is triggering it around 57mph to downshift, whether speeding up or slowing down. I replaced the transmission output speed sensor on the rear of the transfer case yesterday thinking that would be the problem. They have a history of failing in this model vehicle, and cause shifting problems (No 1st, 4th, or OD gears, etc.). Well, that $50 did nothing for this problem, though I do have a new speed sensor that I won't have to worry about for a while!

I also noticed that the transfer case was low on fluid, so I drained and filled it.

Anyone have any other ideas? I just recently purchased this vehicle, and it was fine for a month or two before this problem started. One thing I noticed is that the transmission fluid appears to be a bit overfilled. Could that cause an issue like this? BTW, The fluid appears to be fairly new and clean. Thanks in advance for any ideas!

[msrjeep]

oh well, no TCM, that would have been easy... sorry for your luck

[ShadMan]

Anyone have any ideas/experience with this? Bueller? Bueller?

[ShadMan]

tubsc66 - Any update? Still happening? Have you had it looked at? Inquiring minds want to know!

[ShadMan]

RESOLUTION!!

Well, I discovered that the sensor I replaced the first time was actually the Vehicle Spped Sensor (VSS) and not the Output Speed Sensor (OSS). I dropped the pan, changed the filter, replaced the OSS, added a few quarts of ATF+3, then flushed the tranny by disconnecting the transmission return line and draining into a bucket while adding new ATF+3 fluid until I noticed a difference in the color of the fluid. I wanted to make sure I completely drained the old fluid out (including torque converter, cooler, etc.) in case the previous owner had used Dexron/Mercron III. Filled to the proper level and test drove. No more erradic shifting!! I don't know if it was the fluid or the sensor, but I would definitely lean toward the sensor. $50 including fluid, filter, sensor, gasket. Sweet!

I was so excited I went ahead and replaced the front rotors and pads! Tomorrow will be fluid drain/fill on the differentials, checking motor compression, changing spark plugs, andmaybe flushing coolant system if I get really bored!

Thanks for the help and suggestions. Upcoming projects are rear drum/disc swap, FIPK, headers (anyone know where I can get them cheap??), and maybe a lift (front-->rear coil spring swap), larger tires, and ring/pinion swap to 3.73 (or possibly 4.11). Keep the suggestions coming!

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