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Thread: Idle Desired Airflow Causes Engine to Die

  1. #1
    Tuner in Training
    Join Date
    Aug 2014
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    22

    Idle Desired Airflow Causes Engine to Die

    Just got a 5.3L swap running today. Mods are 5.3L, FAST 90MM intake/TB, LS3 MAF/IAT, 235/242 .621"/.592" 111+3. The car starts and idles but the idle desired airflow keeps walking down to the point that the IAC closes enough and the car stalls. I messed with the base running airflow tables and no matter what, the desired airflow kept walking down to the point of causing the car to stall. o2 sensors arent wired up yet so it's just running open loop. I was wondering if I need to subtract airflow out of the MAF table in the idle region I'm seeing since clearly there is less airflow travelling into the engine than the MAF thinks? I've posted the tune and a log file.
    Drivability.Layout.xml21stcrank.hplmiata_WS6_tune_8.hpt

  2. #2
    Senior Tuner
    Join Date
    Mar 2011
    Location
    Ripley, MS
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    1,865
    There are several things that need to be changed.
    You need to get the wide band working. It's stuck at 11.4 AF Ratio.
    Once you get it working, then you can start tuning.

    The MAF isn't properly failed.
    You need to change the Max Fail freq to 0.
    Then change P0101, 102 and 103 to MIL on first error.

    At that point, you can get the VE table properly dialed in.

    After it's dialed in, then you can adjust the throttle body opening to properly dial in the IAC.
    The IAC should be in the 40-60 once warmed up and in neutral.

    Other than that, I would 0 the traction control tables, as they will affect your ignition timing during the tuning process.

    You can add a few degrees of ignition timing at idle. With that cam, start around 22 degrees or so.

    Change your over and underspeed timing tables to a max of -8 and +8 degrees and ramp down to 0 at 0 rpm error.

  3. #3
    Tuner in Training
    Join Date
    Aug 2014
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    22
    Kevin, thanks for the reply. I was helping a friend get the car running and the exhaust didn't have a bung in it yet(currently open header). The goal was just to get the car running yesterday. I can fail the MAF next time. If you look at the idle spark surface, I already bumped it up to 24*. I think possibly the overspeed spark tables were pulling some spark out and thats why the log shows it at about 18*. My main question is what sensors/calculations feed into "idle desired air"? If the MAF is plugged in, is just the air flow thats calibrated for that MAF frequency? When the MAF is unplugged, is it just the air flow calculated from the VE? Sorry for the somewhat basic questions, I was just confused yesterday how I kept upping the base running airflow without any real influence on the IAC position.

  4. #4
    Tuner in Training
    Join Date
    Oct 2017
    Posts
    11
    Afternoon,
    Dealing with a similar issue with a DBW 5.3 and 0.585/0.585 cam, where the throttle body hunts with a set idle RPM and Spark. Can't get the throttle body to stop oscillating .

    Quick questions:
    1) Why use Over and Under speed settings when there are Idle RPM Adaptives? Could you zero out the Over and Under speed tables?
    2) What is the purpose of zero-ing out the Traction Control Tables?

    thanks.