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Thread: Boost with a 1bar map sensor

  1. #1
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    Default Boost with a 1bar map sensor

    Hi I'm really new to the GM stuff (in my shop we mostly do mustang and honda) so please don't fame me I'm a real newbie. I have done a lot of reading but its not all clear.

    We started experimenting on a trailblaser ss E67 with a magnacharger on it and I would like to ask some question

    How come on a GM there is several tune for blowers application that dosent require a 2bar map sensor?

    How can you adjust the VE table If you only half of it?

    Is this the Maf that do the work at wot ?

    Is there a way to use only the maf and no map like on a ford ?

    Why dose the maf is separate between low and hi? How do the computer know want to change?

  2. #2
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    Use the 2 Bar VVE instead of the 1 Bar VVE.

    Dont know about the MAF, usually with FI a lot of people remove it and go SD. You can run OL-MAF, but you probably will not be able to get it as driveable as you'd like.

    Using a 2Bar MAP is a good idea, I would recommend one for your TBSS.

    Read the VVE Tutorial included with the EFILive download (in Tune or Scan click Help->Tutorials then click Virtual VE Tutorial.pdf.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, tuned, turbo mods, etc.
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  3. #3
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    But why is it an option to use a 2bar sensor?

    How can the computer know if he is in boost if you only have a 1bar sensor on the motor?

  4. #4
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    You are just rescaling the VVE table to have good values past 1Bar, the ECM can do up to 3Bar from the factory. The ECM will know its in boost once it sees airflow values over 14.7psi aka 1Bar, no way a regular NA motor can push more than barometric pressure, it would defy physics.

    It is an option in the E67 to use a 2 Bar sensor because cars like the supercharged Caddy CTS-V use it to control the s/c.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, tuned, turbo mods, etc.
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  5. #5
    Joe (Moderator) joecar's Avatar
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    Hi franckrem, welcome to the forum...

    It may be optional to use a 2 bar or 3 bar sensor... but it is the "right" thing to do.

    Each E38/E67 file can have the virtual VE table be configured to be either 1, 2, or 3 bar... you have the whole VVE table as long as you configured the right one and use the matching MAP sensor.

    It looks to me like the low and high MAF tables don't overlap, the low table max Hz is the high table min Hz (i.e. the same value)... this is the ECM's Hz threshold between the 2 tables.

    I don't know with E38/E67 if the ECM can run MAF-only...?

    Like Erik said, the E38/E67 PCM's are very smart.

    Did you find the VVE tutorial that Erik mentioned...?

  6. #6
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    Yes I found the tables but do I need to tell the computer witch table to use or it will chose it on is own?

  7. #7
    Joe (Moderator) joecar's Avatar
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    There are 4 operating situations:
    - IMTV open (no AFM),
    - IMTV closed (no AFM),
    - IMTV open with AFM;
    - IMTV closed with AFM,

    In each of those there is:
    - one table of VE polynomial coeeficients (the real VE table, but in mathematical form)...
    - three virtual VE (VVE) tables (1, 2, 3 bar);

    whichever VVE table you manipulate is how the real VE polynomial table gets configured.

    If you have no IMTV and no AFM, then the default is the first of the operating situations listed above.

    This is my understanding of it.

    More info: showthread.php?t=8961
    Last edited by joecar; April 25th, 2014 at 01:49 PM.

  8. #8
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    I dield in the fuel injectors today and it seems not that far off... the bigest problem I have is that the transmision dosent want to cooperate it seems to fall in neutral at 5500 rpm from 1st to 2nd

    it was working fine before the blower

    do you guys have any clues?

  9. #9
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    Have you pulled the TCM file and have played with shift times and line pressures? Is the trans built? If not, I wouldnt expect it to last more than a month tops with the Maggie on there.

    I havent heard of a trans simply dropping into neutral unless there's a physical problem...
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, tuned, turbo mods, etc.
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  10. #10
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    It seems to drop in neutral but as soon let off the throttle it shift in 2nd
    almost like its stuck in 1rst...

    should I pull the tcm out even if I dont care about the shift point and firmness?

    would it help to make it last longer?

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