6.5 turbo no overdrive 4L80
 

Took my truck to the transmission shop cuz it would not shift into od they said the tcm was bad 400.00 later and 3 miles and it quit shifting again. found loose battery cable on pass side fixed that everything worked great for about 3 weeks. I can unplug and blow out the tcm it will shift great as long as you drive like granny. first time you get on it shifts real hard and i lose od please help

check your voltage. thats what mine did when i had electrical problems.

what voltage should i have and where should i check it at thanks:argh:

my whole system was low. batteries were barely charging. I'd check it at the batteries. I never did fix it all the way so I can't tell you for sure what it might be i did my motor swap before I fixed that electrical problem. but its an actual function of the ECM to disable overdrive on low voltage.

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waitwaitwait you have a 92?
I didn't notice but I just read up a bit and it looks like it works about the same so since that was one of your problems I would run with it.

Check your Throttle Position Sensor (TPS) plug on the side of your fuel injection pump for loose connection and if it seems tight and clean put some dielectric grease on it. I had that same problem and it would go for weeks and then just quit having OD, put dielectric grease on it and went no problems ever again.

where you livin? If you down here I'm free to help jiggle wires. :U:

check your pedal tps as well they tend to go bad as well and the won't shift, i had that problem before i did my swap in my truck:tttt:

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you also might want to check your speed sensors in the input side of your trans and the output on the tailshaft of the trans and if it is 4x4 check the output speed sensor on your transfer case. i had 2 sensors go bad on mine. they would read onetime and act up once in a while. the sensors are cheap from napa, but i noticed the gm ones are better.:U:

i tried the grease it didnt work it worked for bout 6 miles i turned around then stopped shifting

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i live in ohio so i doubt you will come here..it would be nice but thats a haul..and yea its a 1992..

Any updates? :pca1:

Since there have been no updates in so long, I'm going to assume that the problem is fixed and am closing this thread. The thread can be re opened if needed.