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Thread: idle fuel efficiency?

  1. #1
    Senior Member
    Join Date
    Jun 2005
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    113

    Default idle fuel efficiency?

    I'm working on a pretty agressive "lean cruise" alternative tune, but have noticed that spending any time at idle means:
    1) my AFR of 15.25 for my idle cells is ignored and the truck goes to 14.6-14.7
    2) spending any time at idle or in stop and go traffic destroys the gains from the aggressive fueling table (3647).

    I mean when I'm sitting still and idling my instant mileage is 0!!

    But seriously, I throw money out the window when I idle with these heads, cam and injectors (my average city mileage is 8.5 -- but it's real city -- 13-20 miles a day in 35mph zones and traffic). I've noticed that there is a open loop lean idle pid (B3607) but when I changed that to 15.5 to allow my custom table to kick in (I'm always in open loop), instead of 14.6-14.7, the truck ran at 13.5 AFR lol.

    Also, my small pulse threshold (B4006) is 2.75ms and at idle, my pulsewidth is 2.4. Can I drop this threshold with impunity? For example, if I set this to 1.9 or so, will I see side-effects such as rough idling, etc.?
    Hello, my name is Erik and I am a horsepower addict...





  2. #2
    Junior Member
    Join Date
    Feb 2006
    Posts
    39

    Default

    I am not as far along as you but am attempting the same end result. It seems that no matter what I do the O2s keep me at 14.7. Changing the switching voltage up or down made no difference. I am wondering if there is a way to fool the pcm with modied o2 voltages?

  3. #3
    Lifetime Member oztracktuning's Avatar
    Join Date
    Nov 2005
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    596

    Default

    What would the ideal compromize AFR be at idle to get good idle economy and not hurt the cats or the engine??
    Oztrack
    EFILive Tuning Consultant

    Worldwide Remote Tuning Service

    2006 NSW Super Street Drag Racing Champion

    www.oztrack.com.au


  4. #4
    Senior Member
    Join Date
    Jun 2005
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    113

    Default

    I have no cats and have forged internals, so I am tryin 15.25-15.5 at idle.
    Hello, my name is Erik and I am a horsepower addict...





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