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Thread: "Accelerator pump" action

  1. #1
    Senior Member PSWired's Avatar
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    Default "Accelerator pump" action

    Can someone explain how the LS1 PCMs provide instant enrichment during throttle transients? I see no tables that relate enrichment to throttle transients, can someone explain it to me?
    1995 GMC Yukon 4WD 4DR
    5.3 "LMG" engine: E85 with AFM
    6L80e 6 speed automatic transmission

  2. #2
    EFILive Reseller ringram's Avatar
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    My thought on this is as follows.
    In a carb you need a shot because the velocity of air doesnt change fast enough to pull more fuel in. However in an efi engine you will be sitting at one point in the VE table next second you are at a much higher point so the system instantly throws the extra fuel in as required by the table, no need for the extra shot as the correct fuel is dumped in immediately (+ any PE enrichment due to TP settings) Of course I may be wrong, but after not seeing anything similar thought that this might explain it...
    Would be interested to hear one way or the other..
    Get EFILive in europe (http://www.efilive.eu).
    2007 Escalade ESV L92 6.2L VVT.
    2014 VF SV LS3 Maloo.

  3. #3
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    That is true but additional fuel still needs to be injected to cover the transition between those points.
    Remember the processor must react to events and no matter how fast it is there is always a delay before it catches up.

    If you map a stand alone system you will be amazed at the amount of accell enrichment is required especially on the 8's.
    \"You Can Never Have Enough Horsepower\"

  4. #4
    EFILive Reseller ringram's Avatar
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    Which then begs the question... where is this in efilive? Or is this table not available for messing with?
    Get EFILive in europe (http://www.efilive.eu).
    2007 Escalade ESV L92 6.2L VVT.
    2014 VF SV LS3 Maloo.

  5. #5
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    I imagine so
    \"You Can Never Have Enough Horsepower\"

  6. #6
    Senior Member PSWired's Avatar
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    I remember such a table being present in my days of tuning the TBI engine in my 95 Yukon- TunerCat had a table in it called "Pump Shot." Differential TPS was the independant variable (in %) and the added injector pulse width in microseconds was the dependant variable. It went from 0-25% if I remember correctly. Any such thing in EFILive?
    1995 GMC Yukon 4WD 4DR
    5.3 "LMG" engine: E85 with AFM
    6L80e 6 speed automatic transmission

  7. #7
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    Not that I have seen
    \"You Can Never Have Enough Horsepower\"

  8. #8
    Senior Member PSWired's Avatar
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    Hopefully one of the developers will chime in here.
    1995 GMC Yukon 4WD 4DR
    5.3 "LMG" engine: E85 with AFM
    6L80e 6 speed automatic transmission

  9. #9
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    Look at the throttle follower tables. These are set up to add extra airflow when the throttle position changes rapidly - like an accelerator pump. The extra "airflow" added to the PCM calculated value results in more fuel being injected.
    2003 Silverado SS
    N/A: 14.257 @ 94.63 mph
    N2O: 13.200 @ 102.3 mph

  10. #10
    EFILive Reseller ringram's Avatar
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    Very cool. Just when I thought I was happy with my tune.. Now I have more things to play with.. Ill have to see if I can "kick start" throttle transitions.
    Get EFILive in europe (http://www.efilive.eu).
    2007 Escalade ESV L92 6.2L VVT.
    2014 VF SV LS3 Maloo.

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