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Thread: spark scatter...what's normal

  1. #1
    boostaholic
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    spark scatter...what's normal

    My car has a very lopey idle. Stock cam etc.

    Got MPScan to work and looking at a bunch of graphs and everything seems normal.

    The spark scatter gage jumps all over the place like crazy. I dont know if that's normal. It will jump from one side of the gage to the other.

    Thoughts?

  2. #2
    Supporting Member Turbo Mopar Contributor zin's Avatar
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    Re: spark scatter...what's normal

    You might be seeing the ECU trying to control the idle, and failing, is the IAC maxed out or stuck in one position?

    The big question is what else is wrong, or was recently changed? Are there vacuum leaks/ broken plastic lines?

    Mike

    - - - Updated - - -

    You might be seeing the ECU trying to control the idle, and failing, is the IAC maxed out or stuck in one position?

    The big question is what else is wrong, or was recently changed? Are there vacuum leaks/ broken plastic lines?

    Mike
    "The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry

    Bad laws are the worst sort of tyranny.
    - Edmund Burke

  3. #3
    boostaholic
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    Re: spark scatter...what's normal

    IAC sits around 26 but there is movement on that number just not much.

  4. #4
    Visit www.boostbutton.com... Turbo Mopar Contributor ShelGame's Avatar
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    Re: spark scatter...what's normal

    That's normal. Spark scatter values can be positive timing or negative.

    Our ECU's try to control the idle speed with spark and fuel primarily. IAC adjustments are a 'last resort' so to speak. The reason being, that with a Speed-Density system, any change in MAP (due to the IAC opening / closing) would get a corresponding PW change for 'transient' fuel.

    A ported head, or higher lift/overlap cam will have an effect on the idle quality, and the spark scatter control would need to be tuned to give a good idle. I don't really have any experience tuning the idle control. It has to be a hands-on car-by-car process to get it right.
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  5. #5
    Boost, it's what's for dinner... Turbo Mopar Staff Aries_Turbo's Avatar
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    Re: spark scatter...what's normal

    How's the fuel mix/adaptives at idle. Fueling has a huge impact on idle.

    Quote Originally Posted by turbovanman
    This one is easy, I have myself to blame, I rush things, don't pay attention to gauges when I should, change to much stuff at once then expect miracles, the list is endless.

  6. #6
    boostaholic
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    Re: spark scatter...what's normal

    What are adaptives called in the list of choices for gauges?

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