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  1. #1

    Default Retarded ignition??

    I have hooked up a ScanGage to my truck and the Ignition timing ranges from -15 to -24. Does this mean ATDC? Would this be a normal reading for a truck with an ECU? My old 85 used to be set slightly advanced at idle and would increase under acceleration.
    Boreal
    96 Chevy K1500 Silverado Shortbed 5.7L

  2. #2
    Jr. Engineer
    Join Date
    Jan 2009
    Location
    Rochester, MN
    Posts
    231

    Default

    I used to have a Grand Prix GTP and I was really into tuning. I think the 98 Grand prixs always read negative numbers for timing, so maybe yours is the same way. Your timing should decrease under acceleration or heavier loads and be high when cruising. My timing goes all the way up to around 50.
    99 Silverado Z71 4.8
    2" Suspension lift (Add-a-leafs and leveling keys)
    Long tube headers with 3" offroad Y-Pipe
    Volant Cold Air Intake with Ram Air Intake Tube
    Jet Mass Air Flow Sensor
    Diablosport Predator Tuner

    Previous Truck:
    97 Suburban K1500
    3" Body lift
    2" Suspension Lift (Add-a-leafs and cranked up torsion bars)
    35" Yokohama M/T's
    K&N Intake
    Airraid Throttle Body Spacer
    Hypertech Programmer
    Dual Flowmasters

  3. #3

    Default

    Thanks for the info. Another question - is a reading of -28 equivalent to -28 degrees ATDC with a timing light?


    Quote Originally Posted by mjalstad View Post
    I used to have a Grand Prix GTP and I was really into tuning. I think the 98 Grand prixs always read negative numbers for timing, so maybe yours is the same way. Your timing should decrease under acceleration or heavier loads and be high when cruising. My timing goes all the way up to around 50.

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