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Thread: Tuned as a 2 bar MAP but is actually a 3 bar

  1. #1
    Junior Member
    Join Date
    Mar 2012
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    40

    Default Tuned as a 2 bar MAP but is actually a 3 bar

    Hi all,

    I have been having troubles starting my supercharged LS1 since day dot and i think i may have worked out what the issue is.
    The car was tuned by a guru and i think the MAP sensor may have been overlooked.
    Overall i am very happy with the tune (480rwhp) but the car doesnt start without touching the throttle pedal and sometimes wont start at all if hot!
    I looked at a few things and found the MAP was reading ~40kPa without the engine running. This should be at around 101kPa as per the manual etc.

    I have a sneaky suspicion the car has had a tune with the wrong MAP scaler in it hence making it hard to start.
    I want to set it right and put the MAP scaler {C6301} to a 3 bar setting =288 but i am worried if i do it will ruin the entire tune.
    Are my fears correct? If i make a change to the scaler so that the MAP reads 101kPa without the engine running instead of ~40kPa it currently reads will it mean i will have to re-tune the entire fuel map again?

    Thanks

    Mark

  2. #2
    Member
    Join Date
    Feb 2008
    Posts
    87

    Default

    When you reset the MAP scaler value you'll need to rework the VE and probably the timing tables as well.
    LQ4, Pro-Flo, heads, Stock48 cam'd, twin TO4E 2001 C5 830rwhp/905rwtq
    2001 GMC RCSB pt88/5.3/4l80e/14 bolt 11.34@123.2 best pass so far with a 1,82 60' @ 13lbs boost

  3. #3
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    27,808

    Default

    By changing the MAP scaler you are now changing the indexing into the columns in the VE and OLFA tables...

    a retune is safer than mathematically shifting/expanding the columns in the VE tables.

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