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Thread: Missing Tach

  1. #1
    Tuner CTX-SLPR's Avatar
    Join Date
    Jan 2008
    Location
    Livermore, CA
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    131

    Missing Tach

    Howdy,

    Does a GTP ECM rely on the white tach wire from the ICM or does it calculate it internally like a Regal did? I took the white wire straight off of the ICM to my Autometer tach (which doesn't show anything weirdly) and the scanner wasn't showing any rpm on the gauge either.

    Just trying to figure it out.

    Thanks,
    Central TEXAS Sleeper
    Experimental Physicist

    Current:
    1964 Riviera (4.1L Buick Turbo6, 4L80E, L67 PCM)
    2012 Hyundai Genesis Sedan (3.8 GDI, 8spd Getrag)
    1998 Chevrolet Suburban K2500 (454, 4L80E)
    SOLD:
    1970 Riviera
    1965 Riviera GS (465 Super Wildcat, SP400) #'s Matching
    1967 Skylark Deluxe
    1997.5 Regal GS

  2. #2
    Tuner
    Join Date
    Mar 2008
    Location
    Waukesha, WI
    Posts
    95
    I don't believe the IP uses that white wire from the ICM, but derives the tach signal from the PCM (much like the fuel level).

    However, you should be seeing something from the white tach signal wire when hooked up to a regular tach.

    On mine, I vaguely remember there were two white wires, and the "right" white wire was present on one side of the plug, but it wasn't on the other...
    2007 Trailblazer SS - LS2 | S256sx + S256sx | E85 | Built 4L80-E
    1991 Olds Cutlass Supreme International Sedan - L67 | GT35R | E85 | Built 4T65-E HD | NO2

  3. #3
    Tuner CTX-SLPR's Avatar
    Join Date
    Jan 2008
    Location
    Livermore, CA
    Posts
    131
    Got the Tach to come up in the scanner, now to figure out why Autometer doesn't read.
    Central TEXAS Sleeper
    Experimental Physicist

    Current:
    1964 Riviera (4.1L Buick Turbo6, 4L80E, L67 PCM)
    2012 Hyundai Genesis Sedan (3.8 GDI, 8spd Getrag)
    1998 Chevrolet Suburban K2500 (454, 4L80E)
    SOLD:
    1970 Riviera
    1965 Riviera GS (465 Super Wildcat, SP400) #'s Matching
    1967 Skylark Deluxe
    1997.5 Regal GS