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Thread: Idle spark out of control! 99 Silverado 6.0 swap

  1. #1

    Idle spark out of control! 99 Silverado 6.0 swap

    I went to help a friend tune the idle on his truck that was a 4.8 and swapped to a 6.0 with a big cam. Not a big deal have done many trucks with the same cam except on this truck the timing will not stay where I want it to unless I use the vcm scanner to add timing with special functions. On idle I?m commanding 18 degrees but it only commands that on startup and after about 5 seconds the timing goes down to between 0-7 which brings the idle down and fluctuates there until the truck dies. I have tried zeroing out tables that adjust spark but have not changed the situation. Also removed all ability to retard timing and nothing. Are there any spark modifiers besides on the spark advance and retard tables? Any help would be great thanks. I am currently charging my laptop so as soon as it is down I?ll upload a log

  2. #2
    Tuner
    Join Date
    Feb 2017
    Location
    Houston Texas
    Posts
    67
    Have you had a chance to pull the Tune and Log. I am curious to see what might be the issue.

  3. #3
    After reviewing the log many time I advised the timing chain be changed as it might be loose or the timing jumped a tooth. They did and the chain jumped a tooth and was super loose. After a new sprocket and new timing chain the truck ran like it should.