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Discussion Starter #1 (Edited)
I have a 1993 GC I6 4.0 with 197,000 (and change) miles. The engine still purrs like a wolverine, but I have one problem that I can't seem to figure out. After running for a while and covering x distance, the transmission will not shift into overdrive. She runs fine for a while after a cold start, but once it's been running for a while it just seems like its trying to get into overdrive but cant do it. In overdrive, as most of you may know, it cruises comfortably around 2,000 rpm's. When it doesn't want to shift, it sticks at about 3,000. If it does make it into overdrive, once I start to decelerate it upshifts hard. If I hit the "O/D off" switch while it is trying to reach overdrive, the rpm's drop just slightly.
I have had numerous suggestions, i.e. the TPS (throttle position sensor) which would be for some reason telling the engine that I am looking for more power than I really need, or telling the transmission to run on a different gear range to keep it from being damaged. Some have suggested that my transmission is screwed and this is just a sign of its inevitable failure in the near future, but this problem has been persisting for over 2 years now, so I think if it were failing it would have sh*t the bed by now.
Im really hoping to get this fixed, because it eats up my gas and it limits me from traveling long distances. Any help is appreciated!
 

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Discussion Starter #3
I had recently read that there was a recall for a Torque Converter Drain Back Valve on the transmission. This part can apparently cause the transmission to overheat and damage the transmission? But wouldn't I be having the problem all the time?
 

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Mine does something like this. After a while of cruising at highway speed, especially on a nice hot day and after a hill or two, my overdrive quits working. The light on the O/D off button will even come on by itself. I got out the service manual (mine is a '95) and it said the TCM will lock out overdrive when the trans temp gets over 250 degrees. Seems about right. After mine seems to cool down, O/D works like normal.

Just a thought. I don't know if this is what is wrong with yours. Maybe put an aux trans cooler in? Always a good upgrade anyway. The factory coolers are only marginal. I have one I'll be putting in this spring before wheeling season starts.
 

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Mine does something like this. After a while of cruising at highway speed, especially on a nice hot day and after a hill or two, my overdrive quits working. The light on the O/D off button will even come on by itself. I got out the service manual (mine is a '95) and it said the TCM will lock out overdrive when the trans temp gets over 250 degrees. Seems about right. After mine seems to cool down, O/D works like normal.

Just a thought. I don't know if this is what is wrong with yours. Maybe put an aux trans cooler in? Always a good upgrade anyway. The factory coolers are only marginal. I have one I'll be putting in this spring before wheeling season starts.
I would get on that soon if I were you!
 

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Complete service, including a fluid and filter change and band set, is in order. While the pan is off test/replace the OD solenoid and replace the temp sensor. You could also drill a hole in the bottom of the pan and install a B&M drain plug kit. This will make the next fluid change much easier. Then install a large auxiliary trans cooler in series with the cooler in the rad.
 

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I had the very same thing happen to me after I bought my ZJ.. After takeing to a tranny shop the SALES man told me I need a tranny rebuild.. The tech that drove my jeep gave me his number and told me to call him that weekend.. After less than one minute under my jeep and a new speed shaft senser my jeep is running and shifting like a new born jeep.. The are 2 sensers on your tranny, One is for the speedomiter, near the tail shaft, the second is further up towards the pan, this senser tells the tranny when to shift at what speed.. REPLACE this one. $45 for the senser at autozone and you should be golden.. Do this before you do anything.. Mine was doing the same thing and I saved $1800 thanks to a honest mechanic.. Let me know how it goes for you..
 
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