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MPG calculation

Discussion in 'Gen 2 Prius Technical Discussion' started by lessgascar, Nov 10, 2007.

  1. lessgascar

    lessgascar New Member

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    Based on my experience with our '07 and some posts I've read, the pips on the gas gauge decrease at an irregular rate. This is my geeky way of saying the gauge sucks!

    But it got me thinking, how does the Prius calculate MPG? Because if it's metering gas consumption the same sloppy way the gauge displays it, then the on board display of MPG could be way off. Does anyone out there know what technique is used to arrive the figure I see on my flashy LCD screen?
     
    #1 lessgascar, Nov 10, 2007
  2. bestmapman

    bestmapman 04, 07 ,08, 09, 10, 16, 21 Prime

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    #2 bestmapman, Nov 10, 2007
  3. richard schumacher

    richard schumacher shortbus driver

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    <div class='quotetop'>QUOTE(manymoremiles @ Nov 10 2007, 11:55 PM) [snapback]537868[/snapback]</div>
    It counts actuations of the fuel injectors. Much more accurate than the tank gauge.
     
    #3 richard schumacher, Nov 11, 2007
  4. Bebopp

    Bebopp New Member

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    <div class='quotetop'>QUOTE(richard schumacher @ Nov 11 2007, 12:20 AM) [snapback]537893[/snapback]</div>
    Do you have the source of this info, and is it from Toyota?
     
    #4 Bebopp, Nov 14, 2007
  5. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(Bebopp @ Nov 14 2007, 02:34 PM) [snapback]539551[/snapback]</div>
    The gas gauge is not really sloppy, but it is reading the level of a tank with a variable capacity. The internal fuel bladder in the U.S. versions of the Prius expand and contract with temperature and use, so the usable volume goes up and down. The gas gauge has no way to correct for this variability.

    Injector timing is indeed how the MFD calculates fuel use. It's the same way any modern fuel injected engine knows how much gas is being squirted into the engine. That, along with the air mass flow meter, is how the fuel ratio is controlled.

    If you want more information, do a Google search of this site and you will find this topic addressed many times.

    Tom
     
    #5 qbee42, Nov 14, 2007
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