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Thread: Idle Spark Settling Below Commanded

  1. #1
    Advanced Tuner CCS86's Avatar
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    Idle Spark Settling Below Commanded

    Hi guys,

    I'm trying to find the missing link as to why my idle spark works its way down so low. I feel like I have touched all related tables, but must be missing something.

    I have tuned the idle airflow and ETC idle angle tables as well. My thought was maybe because of more than anticipated air, it is using spark to keep RPM on target, but I have observed the low spark value even with slight positive idle air trim.








    idle-spark2.jpg


    idle-spark-tables.jpg

  2. #2
    Quote Originally Posted by CCS86 View Post
    Hi guys,

    I'm trying to find the missing link as to why my idle spark works its way down so low. I feel like I have touched all related tables, but must be missing something.

    I have tuned the idle airflow and ETC idle angle tables as well. My thought was maybe because of more than anticipated air, it is using spark to keep RPM on target, but I have observed the low spark value even with slight positive idle air trim.

    What's your desired idle rpm? Is it reaching it? -10 ft. lbs seems it's trying to decelerate..

    I would think more air (and subsequently more fuel) into the engine would make the spark lower and vice versa.

  3. #3
    Advanced Tuner CCS86's Avatar
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    Idle setpoint is 800 rpm.

  4. #4
    Advanced Tuner CCS86's Avatar
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    I tried a couple tests today.

    First I reduced the idle airflow table by 25%.

    Next, on top of the first change, I reduced the ETC Idle Throttle Angle table by 20%.

    Neither test netted a change in the idle spark at all. Interestingly, the short term idle trim value didn't change either, and it stayed at +/- 0.02. I definitely would have expected a change here. If the idle air trim isn't based on the idle air table, then what?

  5. #5
    Advanced Tuner CCS86's Avatar
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    Here is my MP0 torque table compared to a stock GT table. I have big reductions in torque in the idle area, which I would think would elevate spark to compensate:

    MP0-TQ.jpg

  6. #6
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    All experience I have is with the 18 5.0's, & GT500 tunes.

    On GT500, the air tables do nothing, to test, put the max values in, see what happens. Lotsa tables in GT500 tune do nothing, one is even said to be airflow, but if you enter say 6, the throttle will open 6 degrees.

    Try to get idle good by adjusting torque tables, that's all that would help mine any at all. Idle spark is only used when idle is not controlled by torque.

  7. #7
    Quote Originally Posted by CCS86 View Post
    I tried a couple tests today.

    First I reduced the idle airflow table by 25%.

    Next, on top of the first change, I reduced the ETC Idle Throttle Angle table by 20%.

    Neither test netted a change in the idle spark at all. Interestingly, the short term idle trim value didn't change either, and it stayed at +/- 0.02. I definitely would have expected a change here. If the idle air trim isn't based on the idle air table, then what?
    I think RPM Ctrl mode is it's own little system unaffected by many things in the tune. If you were in dashpot mode I bet you would have saw a difference.

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    What does your inverse table look like? What is engine brake torque and torque request showing in this screen shot?

  9. #9
    Advanced Tuner CCS86's Avatar
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    Quote Originally Posted by Thatwhite5.0 View Post
    What does your inverse table look like? What is engine brake torque and torque request showing in this screen shot?



    MP0-TQ-INV.jpg



    idle-cond.jpg

  10. #10
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    There's a switch for if it uses torque or airflow tables for idle control if you're talking 11-14 cars. You can disable torque based and use airflow. If I remember right you have to lower the airflow amount to enable dashpot also. I haven't messed with it for a while.

  11. #11
    Advanced Tuner CCS86's Avatar
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    Are you talking about the TQ based decel switch? I don't see anything specific to idle control in my calibration (2012 GT FPDX)