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Thread: B4005 Small Pulse Adjust How does GM create this table?

  1. #11
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    no, area is fuelmass, b4005 is time.

    if the pcm tells the injectors to dump let's say 2.5ms of fuel, it will get less than that, because the injector at first doesnt flow at all, and then it flows less then the official 'static' flow rate. short pulse adder is the amount of time that's needed to make up for that by artificially telling the injectors to open longer than they would have to open for if they provided a perfectly linear flowrate.

    ok, here's a pic, it should be easier to visualize. area under the red curve is going to be bigger than the blue curve. thus we must make the red curve longer to effectively make up for what the blue is missing.

    Last edited by redhardsupra; July 18th, 2007 at 06:44 AM.

  2. #12
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    This is helping tons! I think I am starting to understand.

  3. #13
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    Ah, I see.

  4. #14
    Joe (Moderator) joecar's Avatar
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    Is the red curve supposed to include the offset at the start...?

  5. #15
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    yes, that's what it would be if the injector would start instantly, hold perfect and closed instantly. that's why it's called theory, and why it's only an estimator for the real thing.

  6. #16
    Lifetime Member SSpdDmon's Avatar
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    If the voltage correction is vacuum referenced kind of like the VE, why do we need it since it's only an adder?

    Also, why does the adder increase with vacuum? I would think more vacuum sucking the fuel out of the injector during decel would require less voltage correction than WOT where manifold vacuum is minimal.

  7. #17
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    Quote Originally Posted by SSpdDmon
    If the voltage correction is vacuum referenced kind of like the VE, why do we need it since it's only an adder?

    Also, why does the adder increase with vacuum? I would think more vacuum sucking the fuel out of the injector during decel would require less voltage correction than WOT where manifold vacuum is minimal.

    That is a good observation about {B3701}.

  8. #18
    Lifetime Member 5.7ute's Avatar
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    Possibly the vaccuum holds injector closed & you need more correction.
    BTW great discussion you have going on here.

  9. #19
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    Quote Originally Posted by SSpdDmon
    If the voltage correction is vacuum referenced kind of like the VE, why do we need it since it's only an adder?

    Also, why does the adder increase with vacuum? I would think more vacuum sucking the fuel out of the injector during decel would require less voltage correction than WOT where manifold vacuum is minimal.

    It's because the injectors (if wide open) would flow much more with a negative pressure on it pulling the fuel out, but the above graph shows how the start up and shut down reduces that flow....so the voltage/kPa table adds it back .

  10. #20
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    Another thing that really skews the SPA table is adding low imp injectors. Low imp injectors open and close much faster than stock high imp injectors and don't need as much offset to get the same area under the curve.

    What gives me heartburn is I've reduced the Minimum Pulse Width to 0.3 and the Default Pulse width to 0.3 and it does not lower the idle pw under the magic 1.8. The SPA and the Voltage Offset tables are adding to something else to create that minimum pw number.

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