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Thread: 6 Spd upshift torque reduction

  1. #1
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    Default 6 Spd upshift torque reduction

    I've got a 2007 LMM Duramax with an exhaust and a mild tune -I've turned off the tq reduction request option in the trans tune which made it shift much better HOWEVER, monitoring "driver demanded torque" and "torque delivered to trans" still shows a reduction of 50-60 ft/lbs in delivered torque when it makes a shift.... you can clearly feel it and it's annoying as hell. Is there any way to eliminate this?

  2. #2
    Lifetime Member GMC-2002-Dmax's Avatar
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    Turning off the tq request is a bad idea, it could over time damage your trans.

    You need to adjust the ecm tune to make it defuel less
    www.mscservices.net


    Tuner of many, many Duramax and Cummins Diesels.


  3. #3
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    Default 6 Spd upshift torque reduction

    You can also reduce the commanded shift time (or bump shift pressure if you turned the learning shift time feature off) for that shift, which is my personal preference. You can get some nice crisp shifts outta the stock hardware balancing TR and shift time/pressure.
    14 GMC Sierra
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    Basic tuning....

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    I already have firmed up the shifts by reducing the desired shift times and we are looking at installing a TransGo JR shift kit HOWEVER, regardless of how nicely the trans shifts, there is still the matter of the VERY annoying power reduction during the shift. This HAS to come as a request from the trans controller to the engine controller and since I have turned off this request in the trans program, there should be no such reduction in power while shifting.... UNLESS there is still another parameter in the program which we do not have access to. Anyone (Paul Blackmore) have any thoughts on this????

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    As stated in post 2, have you disabled defuel in the ECM?
    ~Erik~
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    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

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    I have removed every limit I can find in the trans AND engine program.... what parameter specifically is "defuel"?

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    Ok, you didnt say that before. Defueling is related to max torque values, if there is a table/parameter that isnt set correctly it will limit the TQ output. I havent done much work with the Allison side, but the ECM has a lot of tables related to TQ control.

    Post your current tunes and stock tunes (ECM+TCM), usually it's something small that gets overlooked.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, tuned, turbo mods, etc.
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  8. #8
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    I know....I've gone through them all and every torque limit in the trans program (including tq/throttle pos) exceeds the tq values set/produced in the engine program. Since the truck, under light accel, lays over BEFORE starting the shift, and the engine program has no way of knowing when a shift is about to occur, the reduction HAS to come about because of a requested tq limit from the trans controller to the engine controller. For instance, during normal accel from a stop, "driver demanded torque" shows 340 ft/lbs as does "delivered torque to transmission" right up until the shift when "delivered torque" drops to 285 ft/lbs during the shift and then returns to match "demanded torque" after the shift.

  9. #9
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    Word of caution to others reading this, disabling the defuel on shifts is HIGHLY NOT RECCOMENDED. And is a GOOD recipe for grenading your trans. This isn't a 4L60E or 4L80E where if the trans gets hung in 2 gears it is no big deal because there are one way clutches. The ALLISON is a clutch to clutch transmission, and one bad timed shift will QUICKLY rip hard parts clean out of the trans. A PROPERLY BUILT trans set up right with a good ECM tune will have virtually no noticeable defuel on the shifts, and will live a LONG life. A fully built trans by the best in the country with a bad tune with no defuel can make for an awfully expensive door chock when it sends your trannies insides into shratnel.
    1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
    DIAMONDEYE 4" exhaust, CORSA muffler, AFE stage 1 dry filter, custom tuning by me, KENNEDY single pump and pump rub kit.

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    Quote Originally Posted by THEFERMANATOR View Post
    Word of caution to others reading this, disabling the defuel on shifts is HIGHLY NOT RECCOMENDED. And is a GOOD recipe for grenading your trans. This isn't a 4L60E or 4L80E where if the trans gets hung in 2 gears it is no big deal because there are one way clutches. The ALLISON is a clutch to clutch transmission, and one bad timed shift will QUICKLY rip hard parts clean out of the trans.
    ????? - ANY transmission with excessive overlap WILL destroy itself - INCLUDING 4L60E's and 4L80E's. The allison in not special.
    A PROPERLY BUILT trans set up right with a good ECM tune will have virtually no noticeable defuel on the shifts, and will live a LONG life. A fully built trans by the best in the country with a bad tune with no defuel can make for an awfully expensive door chock when it sends your trannies insides into shratnel.
    So..... a trans can have no "defuel" and live but if it has no "defuel" it won't live. You might want to re-think that statement.
    In a diesel engine, fuel IS torque. They are directly linked. To reduce one is to reduce the other. It is a function controlled solely by the ECM and TCM working in unison or the ECM on it's own - the ECM to control max stress on the engine or as RPM/speed control. The TCM requests the ECM to "defuel" to protect the transmission's mechanical limits. Whether the trans is built or not has NOTHING to do with the fact that I have a TCM requesting a reduction in torque from the ECM during light throttle shifts despite the fact that I have removed all visible means of doing so from BOTH the ECM and TCM programming. THAT is the reason I have posted here.

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