Transmission issues

cory99

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Not sure where to look next having hard shifts with my 96 7.3 especially 1-2 if just cruising. If put it to the floor the 1-2 shift is smooth. Also when cruising around 60 the speedometer jumps around a mile or two continuously I tried a vss but still the same. Not sure if problem is related or not and also was noticing it will shift 1-2 then seems like tc locks and drops few hundred then to 3 etc. Starting to wonder if tc isn't going out and causing some of problems since it did want to lock and unlock in between the 3-4 shift as well.
 

Mark Kovalsky

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The first step is to read the codes.

The bouncing speedo could be a PSOM problem, and the PCM gets it's vehicle speed information from the PSOM.
 

cory99

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Ill havr to hook up ae and see if get any codes last time I didn't. I did get a od light flash last year but wasnt around laptop and speedometer bounce was worse so figured was vss ans changed it and unhooked batteries. Stuoid mistake since wasnt around my laptop nut should have left code stored.
 

cory99

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I also swapped rear ends in between and truck acts and with both and two different vss. Is there a bedt way to test vss wiring?
 
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Mark Kovalsky

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With the VSS and the PCM unplugged check for continuity in VSS wires from end to end. Also check each for short to grounds and short to power.
 

rrchlin

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My 96 kinda runs like that. I think 2-3 or 3-4 is kinda rough but definitely smooth if you get on it. Also the shift at 40-45 drops to like 1200 RPM and loses all boost and takes a good while to get up to 50 where it smooths out.

I've been thinking torque converter at 280k but I'm waiting on injectors to see how it shifts once its back to 100% stock power. After reading about CPS sensors and timing today, I wonder how that effects shifting. I purchased a new one today. I also swapped rears from 3.55 to 4.10 and it kinda of shifts better since at a higher RPM I think.
 

cory99

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Thanks Mark will try testing wiring, think I got a used psom around that may try as well if no luck on wiring.
 

cory99

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Mark- my diagram I have has #58 GY/BK for vss. Where does the other wire ground at or will both be on the pcm connector.
 
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needen$77

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Mark are these issues you're talking about could they also show a speedometer go-max past 80 and have a transmission overdrive light flashing

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needen$77

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And also i just noticed it seems like the TQ is locking up immediately on take off and shifts

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Mark Kovalsky

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I think you're getting bad vehicle speed data sent to the PCM. Usually that'a PSOM problem, but it could be VSS wiring, or even a bad VSS.
 

needen$77

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Okay I read the other comments and I'll check in on the wiring then go from there thank you very much

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