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Thread: 4wd 4L60/np241 OSS vs VSS HELP

  1. #1
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    Default 4wd 4L60/np241 OSS vs VSS HELP

    I'm finishing up another swap (lm7/4L60) out of a 2001 silverado (red/blue) with an older pass side drop np241 tcase out of an 80s truck. tcase has a mechanical output which i used a Dakota Digital SEN-01-4160 sending unit to output to the pcm. Right now the vehicle will not shift out of first gear.

    What I have done so far:
    swapped my mechanical green/blue to red/blue computer (re-pinned iac, map and tps, re-wired O2 sensors)
    double checked vss pin outs
    swapped transmissions
    ohm'ed out DD output 0-5
    Tune is from a reputable tuner (same tuned i used in a similar swap but IT had an oem silverado tcase) figured it would be a good base tune
    *****reading my snap on Solus Edge, i can see output shaft speed with correlates with if i unplug the vss pigtail but NOTHING reading vehicle speed

    so i can read output shaft speed but not vehicle speed
    vehicle speed show 1 mph
    I can command shift the trans
    if i manually shift the trans from first to second, its good. if i shift from second to third, the trans shifts back to first

    I have a feeling this is something stupid. Has anyone come across something like this???

    Thank you for your help.

  2. #2
    Joe (Moderator) joecar's Avatar
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    Where is VSS sensor located, and is its wiring ok...?

  3. #3
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    VSS is located on the tcase. Wiring seems good to the best of my knowledge and tested good

  4. #4
    Joe (Moderator) joecar's Avatar
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    PCM needs VSS for looking up the upshift/downshift TPS-vs-MPH tables...

  5. #5
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    I'm hooked into the gm vss wires but im seeing it on my snap on as output shaft speed and not in the vss. Ive set this up a few time this was with no problem.

    Is there a output shaft speed table in EFI?

  6. #6
    Joe (Moderator) joecar's Avatar
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    Try the pid GM.TOS.

  7. #7
    Lifetime Member ProperTuningOG's Avatar
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    The 8K pulse is if its 1 to 1 drive. Most cable driven had a reduction at the gear turning the 8 pulse per output rev to more like 2 or 3. Now you cant just change the pulses you have to change the output shaft to match as well. Sounds like its setup wrong in the tune if you are reading a signal. I've run this sender on many NP208 swapped rigs and its more involved than changing pulse per rev.

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