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Thread: Logging inferred/virtual fuel composition ??

  1. #1
    Potential Tuner Speey_Mikey's Avatar
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    Logging inferred/virtual fuel composition ??

    I'm noticing in my logs the spark advance is always 5-12* higher than what the high octane table says it should be. My hunch is the computer is assuming ethanol content in the fuel and adding timing, but I want to know for sure. Is there a PID that tracks inferred/virtual fuel composition? What else could I look to know why timing is being added? I'm seeing some KR when the timing advances too far and I want to adjust whatever modifier is adding the timing. (2011 Silverado E38)
    Last edited by Speey_Mikey; 11-21-2019 at 08:11 AM. Reason: more info
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  2. #2
    Tuning Addict 5FDP's Avatar
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    There are several spark correction tables that can add or remove timing. Anything from IAT temps to coolant temps and even the commanded EQ ratio in the calibration. If you have VVT that could also be doing something.


    All of those things can be logged. You can log ethanol/alcohol content. Same with all those spark correction tables, that way it can show what it adding or removing timing.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Log everything with the word "advance" or "retard" in the list of available channels and you'll find out what's doing it pretty quickly. Could be PE/COT modifier, could be IAT, ECT, all kinds of stuff.. might be Ethanol content. There's an easy way to find out though.
    Post a log and tune if you want help

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    Potential Tuner Speey_Mikey's Avatar
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    Quote Originally Posted by 5FDP View Post
    There are several spark correction tables that can add or remove timing. Anything from IAT temps to coolant temps and even the commanded EQ ratio in the calibration. If you have VVT that could also be doing something.


    All of those things can be logged. You can log ethanol/alcohol content. Same with all those spark correction tables, that way it can show what it adding or removing timing.
    Quote Originally Posted by schpenxel View Post
    Log everything with the word "advance" or "retard" in the list of available channels and you'll find out what's doing it pretty quickly. Could be PE/COT modifier, could be IAT, ECT, all kinds of stuff.. might be Ethanol content. There's an easy way to find out though.
    Thanks for the advice. I know there are lots of things can impact timing. Looking at the common ones and their multipliers though, I can't make them add up to 12* like I'm seeing at times. Looking for any 'advance' or 'retard' PIDs to logis a great idea. I forget how versatile VCM can be.

    What is the PID to log the virtual ethanol content? The only ones I can find show 4.3% no matter what fuel I put in it. Even with a full tank of e85, it doesn't change.
    Last edited by Speey_Mikey; 11-22-2019 at 05:36 AM. Reason: clarification
    Yes, my username is an unfortunate typo... Just call me 'Fat-Fingers'.

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  5. #5
    Tuning Addict 5FDP's Avatar
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    There isn't a special channel to log for alcohol content. I usually log both channels for ethanol/alcohol content.

    The virtual sensors are known to not work right even if the setting is set to enabled in the tune.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.