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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

    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?



  2. #2
    Join Date
    Feb 2008


    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


    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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