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Thread: VCM bi directional IAC control

  1. #1
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    VCM bi directional IAC control

    Hey guys,

    I'm trying to figure out if I need to change the IAC steps vs effective area and/or max IAC counts on my LT1 24x conversion. I was going to use the bi directional IAC control. Why can I only get 127 steps max? Why can I only command 1200rpm? Neither of these allow me to test the max counts of the IAC to see if the IAC stops working above 255 steps which was the max the LT1 pcm would command.

    Thanks,
    Jason

  2. #2
    HP Tuners Owner Keith@HPTuners's Avatar
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    Probably a limit of the actual control function.
    We got this guy Not Sure, ...

  3. #3
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    I've never seen an 8051 (LT1 OBD1 flash PCM) that could command more than 160 steps.
    2010 Camaro SS M6. Stock Bottom End, Heads/Cam/Intake/Headers/Exhaust.
    2005 Silverado RCSB. Forged 370 LQ9/Borg-Forced Inductions T6 S484/Jake's Stage 4 4L80E with D3 Brake/4WD.
    2023 Durango Hellcat

  4. #4
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    This is a 24X 0411 conversion. Which should be good to at least 310 steps. Right? I can see it command that high when the PCM is controlling the idle.

    limit of the control function?

    Thanks,
    Jason
    Last edited by JasonS5555; 12-01-2014 at 12:03 PM.

  5. #5
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    Quote Originally Posted by JasonS5555 View Post
    to see if the IAC stops working above 255 steps which was the max the LT1 pcm would command.
    Quote Originally Posted by MikeOD View Post
    I've never seen an 8051 (LT1 OBD1 flash PCM) that could command more than 160 steps.
    Quote Originally Posted by JasonS5555 View Post
    This is a 24X 0411 conversion. Which should be good to at least 310 steps. Right? I can see it command that high when the PCM is controlling the idle.

    limit of the control function?

    Thanks,
    Jason
    I wasn't commenting on what the 0411 conversion should command, I was pointing out that the original LT1 PCM, which you mentioned first, the 8051, could command 0-160 on the IAC stepper motor.

    By limit of the control function, Keith means limit of the bidirectional controls. It's not a limit HPTuners imposed, it's a limit GM imposed in the PCM. The 0411 PCM can command more than 127, but it will not allow you to do so with bidirectional controls.
    2010 Camaro SS M6. Stock Bottom End, Heads/Cam/Intake/Headers/Exhaust.
    2005 Silverado RCSB. Forged 370 LQ9/Borg-Forced Inductions T6 S484/Jake's Stage 4 4L80E with D3 Brake/4WD.
    2023 Durango Hellcat

  6. #6
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    Yeah, I was aware of the 8051 = 160 and 411 = 310+ According to some of the tuning software I've seen, the 8051 had a "max" number of steps = 255 and the 0411 had a max steps = 365

    Got it.

    So any idea on how I test to see if in fact the LT1 IAC hardware actually goes past 160, and if so how far? I'm trying to get a handle on how much I can use w/regard to idle tuning.

    Then I'll turn my attention to trying to calibrate the LT1 TB IAC area

    Thanks
    Jason
    Last edited by JasonS5555; 12-01-2014 at 04:25 PM.

  7. #7
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    maybe jack up the throttle follower and cracker?
    1994 Trans Am: LS3 Crate Swap - Cam Motion 216/226-116+3 - 0411 PCM with Lingenfelter 58x > 24x Converter - 4L60E to RPM T56 - Strange 12 Bolt - UMI Suspension - TSP 1 7/8" Headers - GMMG Exhaust

  8. #8
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    Quote Originally Posted by JasonS5555 View Post
    Yeah, I was aware of the 8051 = 160 and 411 = 310+ According to some of the tuning software I've seen, the 8051 had a "max" number of steps = 255 and the 0411 had a max steps = 365

    Got it.

    So any idea on how I test to see if in fact the LT1 IAC hardware actually goes past 160, and if so how far? I'm trying to get a handle on how much I can use w/regard to idle tuning.

    Then I'll turn my attention to trying to calibrate the LT1 TB IAC area

    Thanks
    Jason
    See if the IAC in a 1994 F-Body is the same replacement PN as it is for a 2002? At that point you'd know what the stepper motor can handle (before the pintle falls out)...I don't know if there's a point where it wouldn't equate to any more airflow though.

    I guess I don't understand why it matters to you. Are you having trouble achieving a stable idle?
    2010 Camaro SS M6. Stock Bottom End, Heads/Cam/Intake/Headers/Exhaust.
    2005 Silverado RCSB. Forged 370 LQ9/Borg-Forced Inductions T6 S484/Jake's Stage 4 4L80E with D3 Brake/4WD.
    2023 Durango Hellcat

  9. #9
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    Hey Mike,

    The IAC is different from what I can tell which isn't too surprising considering the differences in TB.

    The IAC is maxed sometimes in the cold and I am having some idle issues. I'm trying to figure out if I need to drill a hole in the TB or modify the tune to account for the differences in IAC area and possibly the count?

    Thanks,
    Jason