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Thread: Difference between Direct and Learned Idle Airflow

  1. #1
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    Default Difference between Direct and Learned Idle Airflow

    I'm trying to better understand direct and learned airflow. Tables and their effect on STIT and LTIT.

    When they are active?
    How do the trims effect them?
    Differences?
    Impact on final idle air flow?
    00 Silverado Z71, LQ9 w/ LS3 heads, BTR cam, Whipple 2.9@8#, 4l80E

  2. #2
    Joe (Moderator) joecar's Avatar
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    You have to read the descriptions of the various idle tables/parameters to link the concepts together...

    ( at this point I'm not sure )

  3. #3
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    Anyone else?

    How about learned airflow correction VS direct airflow correction?

    The fields are the same, except direct airflow correction has two additional columns for AC on/off for a total of 6.
    00 Silverado Z71, LQ9 w/ LS3 heads, BTR cam, Whipple 2.9@8#, 4l80E

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    So I think I figured most of this out, see below:

    B4515 - Direct Airflow IS Proportional idle - makes direct airflow adjustment based on error over B4509.
    B4514 - Learned Airflow IS Integral idle - updates learned airflow based on error over B4508. This value is added to desired airflow based on conditions.
    B4512 - Filtered RPM Airflow Correction IS Derivative. Looks at rate of change as errors approaches 0.

    If anyone has anything to add in, feel free.
    00 Silverado Z71, LQ9 w/ LS3 heads, BTR cam, Whipple 2.9@8#, 4l80E

  5. #5
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by LastCall View Post
    So I think I figured most of this out, see below:

    B4515 - Direct Airflow IS Proportional idle - makes direct airflow adjustment based on error over B4509.
    B4514 - Learned Airflow IS Integral idle - updates learned airflow based on error over B4508. This value is added to desired airflow based on conditions.
    B4512 - Filtered RPM Airflow Correction IS Derivative. Looks at rate of change as errors approaches 0.

    If anyone has anything to add in, feel free.
    Good job

    after you posted this thread (you can see my knowledge level of it in post #2, in between the parentheses), I started reading and re-readingall the descriptions for the idle tables/parameters, it did make my head spin in 3 planes...

    I really appreciate you sharing your conclusions, thanks I will sticky this thread.

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