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Thread: 8051 ECM, change to 8 pulse VSS,just change in TunerPro?

  1. #1
    Carb and Points!
    Join Date
    Feb 2015

    8051 ECM, change to 8 pulse VSS,just change in TunerPro?

    Digging through the factory bin that I have loaded right now in TunerPro on an 8051 ECM for my LT1. The motor/EFI is currently installed in a '62 IH Scout, with an old school SM465 4 speed manual, and a NP205 transfer case. The case is currently set up for a mechanical speedometer, which obviously doesn't work with the EFI.

    I noticed there is a "Speed Pulses Per Driveshaft Revolution" scalar in TunerPro, currently set to 40. Which makes sense, as the stock sensor in the original application would have used the 40 pulse per revolution VSS (computer is from a '94 Caprice 9C1).

    I see Dakota Digital has a 40 pulse speedo drive adapter with factory style socket for $120, and a much cheaper 8 pulse adapter for about $30. Since I don't need the factory socket, can I use the cheaper one and just change the Speed Pulses value in TunerPro to 8?

    I also noticed the 40 pulse adapter is a 3 terminal plug, whereas the 8 pulse is a 2 terminal. Is there another reason I would need that 3rd terminal?

  2. #2
    Join Date
    May 2011
    Lakes Region, NH
    The OEM 40 pulse should be a two terminal sensor, no? The three terminal sensors are known as "reed type" which produce a nice, square wave output while the two terminal sensors produce an a/c signal. The three terminal sensors typically have power, ground, and signal wires while the a/c type have two signal wires to carry the alternating current. I don't know the 8051 wiring pinouts so I cannot advise as to whether that pcm will accept both types of signals directly.

  3. #3
    Fuel Injected!
    Join Date
    Oct 2013
    I think the DD sensor is a 2-wire AC sensor compatible with the stock sensor. I'm not sure what you're looking at, but the '8051 uses a 2-wire VSS.

    It's not as easy as just changing from 40 to 8. The 40 is pulses per driveshaft rotation. The 8 is pulses per speedometer cable rotation so you'd have to use the speedometer gear ratio to determine pulses per driveshaft rotation.

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