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Thread: Quick question about Long Term Fuel trims

  1. #1
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    Default Quick question about Long Term Fuel trims

    If Long term trim reads -7.20 then my computer pulled 7.20 % from the fuel.
    another words it was running rich. If Commanded AFR was 14.63 or Equiv 1.0, then I was running at 13.57 or .928EQ. Did I interpret the data correctly?
    Ed

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    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
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    Quote Originally Posted by BRD-PREY View Post
    If Long term trim reads -7.20 then my computer pulled 7.20 % from the fuel.
    another words it was running rich. If Commanded AFR was 14.63 or Equiv 1.0, then I was running at 13.57 or .928EQ. Did I interpret the data correctly?
    Ed
    Ed, you have the general premise correct, with one big exception. The PCM has had to decrease the Injector pulse width by an average of 7.20% to remain stoich.

    So, in reality your AFR stayed stoich..fuel was just pulled to keep you stoich. Your AFR would not go to 13.57..it would still be ~14.63..
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


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    Joe (Moderator) joecar's Avatar
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    It would have run rich if the trim did not correct it... so like Shawn said it stayed at stoich (it is not rich because the trim prevented it from going rich as soon as it started to go rich).

    It means your airmass calculation is 7% too much air.

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    Lifetime Member mr.prick's Avatar
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    What injectors are you using?
    512k RoadRunner Firmware 12.14R
    FlashScan V2 Bootblock V2.07.04 Firmware V2.07.22 EFILive V7.5.7 (Build 191) V8.2.1 (Build 181)
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    stock injectors, I'm in the process of recalibrating a 100mm maf for a custom air box. Interesting is the fact the table I got for the MAF guy Bruce at POWRMAF were way under what ended up being close. I'm still tuning but if someone is interested then I will post the custom Ram air box and MAF setup with more specifics.

    Thanks for your answers I just miss typed I knew the PCM drove it to Stoich. I just want to make sure which direction and the proportional part. In short I'm going to lower my air flow at the MAF freq that had lower (-) numbers (richer) by the percent of the LTTrim and raise the air flow at the freq that had positive numbers.
    PS my B120(?) MAF only rpm normally set at 4000 I have set to 600 rpm so my trim should only be based on maf numbers right?
    Ed

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    Joe (Moderator) joecar's Avatar
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    Yes, from 600 and above it is using MAF only.

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    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
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    I don't use LTFT % (BENS) for the 'upper portion of the MAF Frequency. That won't be accurate.

    Its very important to maintain the 'slope' of the entire MAF curve, or your WOT fueling can be way off. For a more advanced discussion, see these Summary Notes: (MAF Tuning): http:///forum.efilive.com/showthread.php?16280-CALC-VET-Summary-Notes
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


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    I have B3647set to what I want for enrichment, B3618: PE Modifier Based on Rpm (EQ): is set to 1.0 . With B0120 set to 600 rpm it will still use table b3647 right?

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    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
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    Quote Originally Posted by BRD-PREY View Post
    I have B3647set to what I want for enrichment, B3618: PE Modifier Based on Rpm (EQ): is set to 1.0 . With B0120 set to 600 rpm it will still use table b3647 right?
    Are you comparing Commanded EQ to Actual via wideband?
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


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    yes, I'm asking if commanded EQ is 1.13 in B3647 for 4400rpm at 80- kPa. Then when my engine is at 4400 rpm 80- kPa even in MAF only mode I still have 1.13 commanded right. Right now all of my PE are set to 1.0. So all of my commanded fueling is a reflection of B3647 if my coolant temp is in range. What I was asking is with VE off by setting b0120 to 600 rpm I'm still driving commanded fuel by B3647 right.
    In summary should I ever have anything other than 1.0 in my PE tables?

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