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Thread: Disabling Short Term Fuel Trim

  1. #1
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    Disabling Short Term Fuel Trim

    I have been at dyno for half of day today and I was unable to achieve more power beyond 5.5K RPM as short term fuel trim would kick in and gradually increase which then rich out AFR from 12.5 to 10.0. Does anybody know how to disable Short term fuel trim, perhaps, it's hidden in a correction table? If not, is that feature hidden?

    Software version is 4.0.6

    Attached is my log file. Please help! I'm also not a professional tuner so go easy on me.

    Thank you,

    Steve
    Attached Files Attached Files

  2. #2
    Senior Tuner BackyardTurbo_FTW's Avatar
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    Post the tune file

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    Quote Originally Posted by BackyardTurbo_FTW View Post
    Post the tune file
    Oops... See attached! After this, I have tried modifying lamda value from 0.7 to 0.82 but haven't dyno yet. Although, short term fuel trim was still kicking in at higher RPM.

    Also, I notice a HP flats out at 5.5K RPM. Is there any to pick up the power from 5.5K and up? I'm assuming it's because after 5.5K short term fuel trim kicks in and rich out AFR which cause the power band to flat out.

  4. #4
    Senior Tuner BackyardTurbo_FTW's Avatar
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    2 problems I see right away.

    You need to set the base lambda table flatter at higher temps to maintain the AFR you want (further negative is higher EGT temps), it tapers to .70. Log delta temperature and you will see you are just commanding a richer AFR as you go thru the pull which is why you see it running richer. Use the files I attached in the next post to log the car, it will show you the STFT isnt making the AFR richer, its actually being commanded richer.

    Second, set the EGT Torque limit table to 100 across the table. Same thing is happening here, as the EGT is rising it is getting richer and pulling power back.


    You're also going to want to raise the wheel tq vs VSS table or you will start hitting power reduction mode when trying to do pulls in lower gears.
    Last edited by BackyardTurbo_FTW; 06-19-2018 at 07:25 AM.

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    Senior Tuner BackyardTurbo_FTW's Avatar
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    Your MAF tuning in general is just way off looking at the log. IMO, I would do the above changes and get the MAF dialed in properly. It makes the trans shift far better also once that's in line Ive found. Try these included channel and layout files to help with that.

    C63_Tuning.Channels.xml

    c63.Layout.xml

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    Quote Originally Posted by BackyardTurbo_FTW View Post
    Your MAF tuning in general is just way off looking at the log. IMO, I would do the above changes and get the MAF dialed in properly. It makes the trans shift far better also once that's in line Ive found. Try these included channel and layout files to help with that.

    C63_Tuning.Channels.xml

    c63.Layout.xml
    Thank you for your detailed input. This is very helpful for me. I have a few questions:

    1) when increasing wheel TQ vs VSS table, should I increase all? Roughly how much should I start to increment? What will I nootice if it's raised too much?

    Thank you,

    Steve

  7. #7
    Senior Tuner BackyardTurbo_FTW's Avatar
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    I haven't found any adverse effects just maxing all the cells except the lowest speed one, which I raised by 25%.

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    Quote Originally Posted by BackyardTurbo_FTW View Post
    I haven't found any adverse effects just maxing all the cells except the lowest speed one, which I raised by 25%.
    I will do some pulls on the street to log data and see if I can feel any differences.

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    Quote Originally Posted by BackyardTurbo_FTW View Post
    Your MAF tuning in general is just way off looking at the log. IMO, I would do the above changes and get the MAF dialed in properly. It makes the trans shift far better also once that's in line Ive found. Try these included channel and layout files to help with that.

    C63_Tuning.Channels.xml

    c63.Layout.xml
    Once I get the AFR to be consistent around 12.8 - 13.0 at WOT, my next step would be MAF tuning.

    Any advise on tuning MAF?

    Anything I should disable or temporary change in order to calibrate MAF or do I simply read MAF bank 1 & 2 ratio based on LTFT + STFT and try to get that to be 0 or 1?

    From idle to 4k RPM I will calibrate MAF based from my scan of the LTFT + STFT ratio. How should I tune MAF when WOT?

  10. #10
    Senior Tuner BackyardTurbo_FTW's Avatar
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    The car seems to run mostly in closed loop all the time so just keep using LT+ST for each side to dial in each MAF table. If you notice the car going into open loop and the actual AFR doesnt match the desired AFR just adjust that cell by the percent that it is off. If you use the config files I posted the charts should help get it in line pretty quickly!

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    Quote Originally Posted by BackyardTurbo_FTW View Post
    The car seems to run mostly in closed loop all the time so just keep using LT+ST for each side to dial in each MAF table. If you notice the car going into open loop and the actual AFR doesnt match the desired AFR just adjust that cell by the percent that it is off. If you use the config files I posted the charts should help get it in line pretty quickly!
    So what the numbers logged from LT+ST, that is percent off? For example, if it shows 10 at 128 microsecond. Do I subtract 10 under 128 microsecond in editor or multiply by .90 to reduce 10 percent from LT+ST log? And if it displays nevative (-) number?

  12. #12
    Senior Tuner BackyardTurbo_FTW's Avatar
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    You can just copy and paste the values from the chart and do a paste special right over the appropriate table in the tune file. It can't be any easier than that

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    Quote Originally Posted by BackyardTurbo_FTW View Post
    You can just copy and paste the values from the chart and do a paste special right over the appropriate table in the tune file. It can't be any easier than that
    I subtracted! No wonder engine was idling like a Barracuda. Lol

    Thanks for your patience and continuous guidance.

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    Quote Originally Posted by Fu03steveC63 View Post
    I subtracted! No wonder engine was idling like a Barracuda. Lol

    Thanks for your patience and continuous guidance.
    I'm a bit concern of entering MAF reading and replace it with existing values. Values are largely differences.

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  16. #16
    Senior Tuner BackyardTurbo_FTW's Avatar
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    You don't replace, you do paste special/multiply by %.

    Make sure you are doing a decent 15-30 min ride so you try and hit every cell multiple times to get the best data for corrections. Then after you flash it, let it warm up and then reset adaptives in scanner before trying to tune the MAF any further. Otherwise you just be chasing your tail!

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    I'll give it a try when my car is repaired. Center console caught on fire and burned the main body harness.