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Thread: Strange speedo behavior after swap to 4L80E

  1. #1
    Tuner in Training
    Join Date
    Oct 2014
    Posts
    48

    Strange speedo behavior after swap to 4L80E

    Hey guys, quick question. I have a 96 Z28 with a turbocharged 5.3. I managed to murder my TH350 and so opted for a boneyard 4L80E. I ordered BP automotive plug and play harness to go from the LT1 based wiring to the necessary 5.3 using a 0411 PCM, opting for a 4L60E trans plug at the time. With the TH350, I just had it zip tied out of the way. When I installed the 4L80E I also bought BP automotive plug n play 4L60E to 4L80E conversion harness. I got that all installed last night and flashed the computer to reflect what I wanted. But the weird thing is, sitting still in park/Neutral, the speedometer shows like 23mph. Now, if I start driving, it instantly reflects how fast I'm really going. Otherwise, it drives and shifts fine.

    Have any ideas or familiarity with that behavior? Thanks in advance.

  2. #2
    Tuner in Training
    Join Date
    Oct 2014
    Posts
    48
    Nevermind. A gent on the HPTuners facebook site saw my question and answered.

    There are 2 speed sensors on the 4L80E. The front one (closest to the front of the transmission, left hand/drivers side) is the ISS sensor for the front drum, while the rear one is the VSS signal. When swapping from a 4L60E to the 4L80E, the existing VSS connector from your main harness goes to the rear sensor while the new 'add on' harness that came with the BP Automotive harness kit goes to the front sensor. Since both connectors are the same dimensionally, I assumed (always dangerous) that it didn't matter which one went where.
    Thanks,





    Quote Originally Posted by mightyquickz28 View Post
    Hey guys, quick question. I have a 96 Z28 with a turbocharged 5.3. I managed to murder my TH350 and so opted for a boneyard 4L80E. I ordered BP automotive plug and play harness to go from the LT1 based wiring to the necessary 5.3 using a 0411 PCM, opting for a 4L60E trans plug at the time. With the TH350, I just had it zip tied out of the way. When I installed the 4L80E I also bought BP automotive plug n play 4L60E to 4L80E conversion harness. I got that all installed last night and flashed the computer to reflect what I wanted. But the weird thing is, sitting still in park/Neutral, the speedometer shows like 23mph. Now, if I start driving, it instantly reflects how fast I'm really going. Otherwise, it drives and shifts fine.

    Have any ideas or familiarity with that behavior? Thanks in advance.