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Thread: Undocumented boost limit on FGX Sprint

  1. #1
    Advanced Tuner 4wheelinls1's Avatar
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    Undocumented boost limit on FGX Sprint

    I have an issue with an FGX sprint that commands lowering boost at higher rpm. I am commanding 18 psi however the boost command drops from 4000 rpm in the log tapering off to 12.5 psi. FG had a wastegate backpressure modifier that HP have never added however you could overcome this bu commanding higher boost than required to offset the multiplier. I was unable to achive this with the sprint as if there is another boost limiter that is missing from the software, all tepm limits are off and noTQ limit is flagged in the log.

  2. #2
    Tuner in Training YoloTuner's Avatar
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    I have tuned 2 Sprints using HP with no issues whata so ever. Try adding some wastegate duty cycle, you have taken out duty cycle for some reason.

    moreduty.PNG

    Why dont you try tuning it in open loop boost first then later on enable closed loop boost control?

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    Advanced Tuner 4wheelinls1's Avatar
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    Quote Originally Posted by YoloTuner View Post
    I have tuned 2 Sprints using HP with no issues whata so ever. Try adding some wastegate duty cycle, you have taken out duty cycle for some reason.

    moreduty.PNG

    Why dont you try tuning it in open loop boost first then later on enable closed loop boost control?
    I did try more wastegate duty and it made no difference, I have logged the duty and backfilled the table with the running values, they will be lower due to the high flow CAT, big dump and larger cooler, my issue is the commanded boost in the log does not match the commanded boost in the table, something is requesting lower boost like and airflow or boost limiter.
    I did not try open loop, I have never run open loop on FG onwards as the PI control is much better and faster than the old BA

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    Advanced Tuner 4wheelinls1's Avatar
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    Are you raising 20342 ETC throttle body air flow? Maybe thats acting as a limiter?

  5. #5
    Tuner in Training YoloTuner's Avatar
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    The way I do it as above is tune it in open loop and compare the duty cycle in my DC table to the duty cycle being logged in my data logger. I also change my multipliers, Turbo DC Mult for Octane, Turbo DC Mult vs. Baro etc and WOT to 1.0. Once im happy that im seeing in my data logger the same duty cycle as Im commanding in my wastegate DC table ill sometimes enable Closed loop boost control if I really have to and the customer insists. As far as 20342 ETC throttle body air flow I see you have changed your Idle airflow and multipliers, not sure why you would do that.

  6. #6
    Advanced Tuner 4wheelinls1's Avatar
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    Quote Originally Posted by YoloTuner View Post
    The way I do it as above is tune it in open loop and compare the duty cycle in my DC table to the duty cycle being logged in my data logger. I also change my multipliers, Turbo DC Mult for Octane, Turbo DC Mult vs. Baro etc and WOT to 1.0. Once im happy that im seeing in my data logger the same duty cycle as Im commanding in my wastegate DC table ill sometimes enable Closed loop boost control if I really have to and the customer insists. As far as 20342 ETC throttle body air flow I see you have changed your Idle airflow and multipliers, not sure why you would do that.
    Funny take the opposite approach and command what i need then log the duty and backfill the table wastgate duty table. Has worked fine like that for over 10 years. Have you got a stock file? This car was 3 months old but had some funky values in it like it was commanding. 67 afr under boost. The owner swears its stick but i have my doubts. I never changed any idle air multipliers.

  7. #7
    Advanced Tuner 4wheelinls1's Avatar
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    I just looked at an SCT stock file, apparently those are the stock commanded AFR's

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    2016 Sprint Fuel Base changes.png

    Fuel base has changed!

  9. #9
    Advanced Tuner 4wheelinls1's Avatar
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    Quote Originally Posted by Grant LS1 View Post
    2016 Sprint Fuel Base changes.png

    Fuel base has changed!
    Yes I changed those, I don't want that rich. I always set the base to what I wish to run then adjust the Mass per Airmass and Tuning correction to acheive the same a the commanded and correct fuel trims. That way the load calculation and TQ is correct. if you have the correct injector data it's usually not far off anyway.