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Thread: Installing a VSS Sensor with Holley EFI

  1. #121

    Default Installing a VSS Sensor with Holley EFI - How to with original TBI optical VSS?

    Quote Originally Posted by Danny Cabral View Post
    Yes, the HP & Dominator ECUs can be wired for a VSS or driveshaft speed sensor (LINK).
    The HP ECU is only compatible with the better, Hall-Effect (digital) "F" Type speed sensors.
    The Dominator ECU is compatible with Hall-Effect (digital) speed sensors, as well as VR Magnetic (inductive) "S" Type pickup speed sensors. (Holley EFI Wiring Manual - Section 9.1 "Inputs", Pages 27 & 28)

    Hall-Effect: 3-wire, square wave signal (digital), pulse generation
    VR Magnetic: 2-wire, sine wave signal (inductive), voltage generation (Hall-Effect vs VR Magnetic)
    Read this post on installing a VSS sensor with either the HP ECU or the Dominator. What isn't clear to me is I have an original '87 TBI truck. The speedometer has an optical VSS in it which generates the 2K PPM as I recall. Not sure if this is considered to be a Hall-Effect or an inductive speed sensor. There is a buffer that attaches to the speedometer that conditions and amplifies the signal, which it then sends to the TBI ECM. I'm not sure if I can just use the output from this to send the signal to the HP or Dominator ECU, or if I need to get something like the Auto Meter 5291.

  2. #122
    Join Date
    Dec 2009


    Quote Originally Posted by hegill View Post
    What isn't clear to me is I have an original '87 TBI truck. The speedometer has an optical VSS in it which generates the 2K PPM as I recall.
    I don't know if Holley EFI is compatible with that type of VSS.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  3. #123


    Here's what the 1987 R/V Manual says:
    "The ECM applies and monitors 12 volts on CKT 437. CKT 437 connects to the Vehicle Speed Sensor (VSS)
    which alternately grounds CKT 437 when drive wheels are turning. This pulsing action takes place about 2000
    times per mile and the ECM will calculate vehicle speed based on the time between "pulses”.

    According to Jaguars That Run, this outputs a square wave signal. Problem is, since the stock ECM determines the speed by calculating the time between the pulses based on a 12V signal it sends to the VSS, I'm not sure how I would tap into this to get the signal. Any ideas?

  4. #124


    I'm in the same boat. I assume we're talking about a 700R4 transmission.

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