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Thread: Crazy LTFTs on decel

  1. 04-20-2017 #1
    355LT1
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    Crazy LTFTs on decel

    Here's the ugly mess I'm in on a total Frankenstein deal that certainly not my doing. Here's what I'm working with.

    95 Firebird with

    6L LQ4 from a chevy van - mild street cam - otherwise bone stock.
    700R-4 Transmission
    MAF from a 6L silverado
    DBC Throttle body
    2001 ECM from a 4.8 Silverado
    ECM transmission segment flash from an M6 ECM of same OS

    So I'm trying to tune but when I go into decel and MAP drops the LTFT go through the roof (+25). Note this car does not have VSS so I really don't know if true DFCO ever gets enabled. Biggest problem is, if those trims stay, the next time I try to start it's crazy rich takes quite a while to clean up. I have tried to Limit the LTFT to 6 by setting Max Learn Limit to 1.06 or so but that function doesn't seem to really work. I've also tried a SD tune but same thing happens.

    Anybody have an idea how I can work around this problem? Is it all because I don't have VSS?

    Any suggestions are appreciated.

    Regards,
    Steve
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  2. 04-20-2017 #2
    Ben Charles
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    Why not disable LTFTs...

    Email Tunes, [email protected]
    96 TA Blown/Stroked, 4L80E/Fab 9
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  3. 04-21-2017 #3
    07GTS
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    u need a VSS
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  4. 04-21-2017 #4
    355LT1
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    I found a work around solution. Since the car has a mild cam, the MAP at idle was in the 40's. So i
    I moved the LTFT Map learn limit from 24KPA up to 35KPA. Problem solved, as soon as I start to decel MAP drops below 35 and learning is disabled. Works like a charm. BTW, even without a VSS it looks like some kind of DFCO is working. My WB AFR's go north of mid 20's during decel. Not sure why or how. Maybe my MAF curve or VE table is dicked up down in those ranges - I honestly didn't spend much time messing with them below idle MAP and MAF's.

    Thanks for the suggestions.

    Regards,
    Steve
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  5. 04-21-2017 #5
    07GTS
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    strange because above a curtain speed is needed for dfco to enable if it's at zero it won't enable, check your ftc number to see what its doing
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  6. 04-21-2017 #6
    355LT1
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    Yea, That's what I thought as well. I confirmed there was no VSS. If I recall it put the crazy trims in Cell 20 or 21 (not sure from memory and deleted the logs) It's must be that my VE and MAF were so screwed in those areas that it just added fuel like crazy. Anyway, The POS is gone back to it's owner. That being said, it's like the friggen boomerang car - keeps coming back. Keeping my fingers crossed!

    Regards,
    Steve
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