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93 K2500 4l60e shifts into 3-4 at high RPMs (4k)

Myrickwr

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Louisiana
Have 93 6 lug K2500 that usually runs pretty smooth.
Current issue came after changing out the radiator and oil cooler lines the transmission wouldn't shift into 3-4 (D-OD). Found a leaking transmission cooler line and replaced it. Still has the same problem. Fluid is good and doesnt smell burned.
Think the A/B solenoid went out. 1-2 are good. ???
If I give a lot of gas it'll rev and shift at about 4k RPM into 3rd and 4th. Downshifts when slowing back down.

Thanks
Rob
 
Haha yeah thx. I believe the pins should read to ground while installed on the truck. Maybe more to it but that's what I've found.

Thx
 
You can test the solenoids by jumping them and measuring amperage flow. Should be around 1amp. You can ohm them out too but amperage flow is a much better test.

Honestly the only way to properly diagnose a electronically controlled transmission is with a scan tool. Check for codes. Check TPS and Speed sensor data on a test drive. Other wise your just throwing money at it.
 
Has no codes. I don’t have an ODBI scan tool I can drive with and verify codes. I don’t want to throw money at it but it seems with 1-2 good and no other symptoms it could be a solenoid that’s gone out.
 
Also, after repairs to radiator and oil cooler lines I went on a short test drive when I noticed the xmsn shifting issues. I came home immediately and checked the xmsn fluid, which was basically empty... Topped off the fluid and looked for leaks, with the truck running found one of the xmsn cooler lines spraying the engine bay. Hence the quick loss of fluid. All that’s changed now but wondering if a solenoid went out with the fluid being lost....obviously I don’t know, my assumption
 
If you ran it low on fluid... you probably damaged the transmission.

The last obd1 I had with issues was a TPS. No check engine light ever. But it was reading zero volts in the scanner. Like I said you NEED a scanner to work on this stuff. Obd1 is notorious for not setting codes for a bad sensor. Only way your going to figure that out is looking at data.
 
My bet is a bad tps. They can go just like you described. All shifting on a tbi is done via vehicle speed, rpm's, and throttle input. A solenoid issue will stop it from shifting, but not normally change when it shifts. If your speedometer is working, then the speed sensor is working(93 4l60e only has 1). I would backprobe your tps as you'll probably find a flat spot in it or a non linear output. Should be around .45 volts +/-.05 at idle and roughly 4.5 volts at wide open throttle with a smooth linear change. Any jumps or twitches in it is a sign of a bad tps.
 
My bet is a bad tps. They can go just like you described. All shifting on a tbi is done via vehicle speed, rpm's, and throttle input. A solenoid issue will stop it from shifting, but not normally change when it shifts. If your speedometer is working, then the speed sensor is working(93 4l60e only has 1). I would backprobe your tps as you'll probably find a flat spot in it or a non linear output. Should be around .45 volts +/-.05 at idle and roughly 4.5 volts at wide open throttle with a smooth linear change. Any jumps or twitches in it is a sign of a bad tps.
Thank you sir. Which pin(s) do I need to probe to read the voltage?
I will look at it this weekend and see what I find. Makes sense as this came outta nowhere.

I'll update what I find
 
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Rings out from .03 to 1.2 VDC at idle with RPMs at about 1200. Thought the high idle was due to the cold snap we had. I'll get a new TPS and see if that does it
 
Your voltage seems very unstable. But you dont need the truck running to test the TPS. Back probe the signal wire then turn the key on. Then press the throttle slowly all the way to WOT and watch the voltage. It should be a clean sweep from .5 to 4.5v. I prefer to graph it to make it easy to find a glitch. Min max mode on your meter will work too. If your voltage is good KOEO but unstable KOER check charging system and wiring.

You could have a good TPS but a bad wire and not catch it testing at the sensor though. If you dont have a scanner testing at the PCM connector is recommended. My opinion is if your going to work on your own truck. A scanner is must have tool now a days. They have become very affordable. Or look for a used Tech2 and have a full factory scan tool which is my choice for these trucks.
 
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