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Thread: AFR While Off Throttle (Coast)

  1. #1
    Senior Member tatasta's Avatar
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    Default AFR While Off Throttle (Coast)

    1999 A4 Trans Am, stock bottom end, H/C/I w/TR224-112, 3400 stall

    Currently running COS5 in OLMAF.

    AFR is running very well in all areas except when I let off the throttle and the car is coasting.

    The AFR goes right to ~12.5:1 when throttle is closed.

    I attached my tune and a piece of log file for reference.

    Thanks
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    Attached Files Attached Files
    1999 Trans Am - P&P LS6 Heads - TR224-112 - Procharger P1SC - Performabuilt Lvl 2 4L60E w/ 2800 Billet Stall - 9" Inch w/ 3.70s - LS6 Intake - Mac Mids - ORY - Gibson Catback - Suspension, Drag Radials, A bunch of Other Stuff

  2. #2
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    No expert but did you look at:
    DFCO deaccel fuel cut off?
    To quote the book "Master EFI Tuner" by Dan Maslic
    Deceleration Fuel Cut-Off, DFCO for short. This function is used primarily to aid in higher fuel economy and lower emissions.
    Throttle Cracker
    Throttle Follower
    They work inconjuntion to reduce the impact of just instantly closing the throttle.
    Transient Fuel Impact Factor
    This adjustment is for how fuel reacts to its environment (during transient period) . It considers intake runner length, air temp, manifold fill times etc. and allows adjustment for fuel effects like boil time etc.. Best to leave alone without the right equipment and knowledge.
    I hope this helped.
    Ed

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    what injectors do you have? most cases of rich-on-decel are a function of not having good characteristics for short pulse fueling.

  4. #4
    Senior Member tatasta's Avatar
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    Quote Originally Posted by redhardsupra View Post
    what injectors do you have? most cases of rich-on-decel are a function of not having good characteristics for short pulse fueling.

    They are 33# @ 3 bar LS1 injectors. I have not changed any tables for them other than adjusting them for proper IFR.

    Any thoughts on where to start on short pulsing adjustments.

    Thanks
    1999 Trans Am - P&P LS6 Heads - TR224-112 - Procharger P1SC - Performabuilt Lvl 2 4L60E w/ 2800 Billet Stall - 9" Inch w/ 3.70s - LS6 Intake - Mac Mids - ORY - Gibson Catback - Suspension, Drag Radials, A bunch of Other Stuff

  5. #5
    Lifetime Member hquick's Avatar
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    B3701 has a VERY big effect on off throttle fuelling.
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

  6. #6
    Senior Member tatasta's Avatar
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    Quote Originally Posted by hquick View Post
    B3701 has a VERY big effect on off throttle fuelling.
    Ok.
    1999 Trans Am - P&P LS6 Heads - TR224-112 - Procharger P1SC - Performabuilt Lvl 2 4L60E w/ 2800 Billet Stall - 9" Inch w/ 3.70s - LS6 Intake - Mac Mids - ORY - Gibson Catback - Suspension, Drag Radials, A bunch of Other Stuff

  7. #7
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    And what would one do with that table to help with this problem?????

    230" Dragster - 2000 LS1, 02020003 Speed Density, PRC 2.5 Heads,
    MS3 Cam 237/242 .603/.609, Vic Jr. intake, Holley 1000CFM TB,
    PowerGlide, 5000 stall converter. 8.70@154 MPH

    My Projects Homepage: http://www.horsepowerracing.com

  8. #8
    Lifetime Member hquick's Avatar
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    I played with this table a LONG time ago.
    From memory...try lowering the numbers slightly in the 9.5-11.5 range and see if it helps. If you're hitting DFCO and it's not cutting fuel properly (ie...it's still kinda flicking on and off) then lowering the values slightly should help.
    I found it made a big difference when I was going very rich on decel.
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

  9. #9
    Senior Member tatasta's Avatar
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    Quote Originally Posted by hquick View Post
    I played with this table a LONG time ago.
    From memory...try lowering the numbers slightly in the 9.5-11.5 range and see if it helps. If you're hitting DFCO and it's not cutting fuel properly (ie...it's still kinda flicking on and off) then lowering the values slightly should help.
    I found it made a big difference when I was going very rich on decel.
    I will take a look at it and report back once I get a chance to try it.

    Thank you
    1999 Trans Am - P&P LS6 Heads - TR224-112 - Procharger P1SC - Performabuilt Lvl 2 4L60E w/ 2800 Billet Stall - 9" Inch w/ 3.70s - LS6 Intake - Mac Mids - ORY - Gibson Catback - Suspension, Drag Radials, A bunch of Other Stuff

  10. #10
    Lifetime Member 5.7ute's Avatar
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    Quote Originally Posted by redhardsupra View Post
    what injectors do you have? most cases of rich-on-decel are a function of not having good characteristics for short pulse fueling.
    X2
    After doing a lot of work on injector characteristics I have found many reasons for the rich decel/idle problems that we face with larger injectors. Injector voltage offsets, small pulse adjust & default pulsewidth seem to be the main culprits.
    look here http://forum.efilive.com/showthread....highlight=IBPW
    and here http://forum.efilive.com/showthread....highlight=IBPW
    The Tremor at AIR

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