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Computer post's lower MPG than it should because of the 99.9 limit?

Discussion in 'Gen 2 Prius Main Forum' started by AndreJ, May 10, 2007.

  1. AndreJ

    AndreJ New Member

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    Computer post's lower MPG than it should because of the 99.9 limit?

    I was wondering if you guys ever considered the fact that the computers only goes up to 99.9 meaning that the average is going to be lower than it should because when running with only the electric motor it is getting way beyond 99.9 MPG, so if im getting 50.2 MPG from the computer, may i actualy be getting the estimated 55 EPA? tell me if im wrong on this cause this sounds right to me. :unsure:
     
    #1 AndreJ, May 10, 2007
  2. adgo82

    adgo82 New Member

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    Where is your math to get that calculation?
     
    #2 adgo82, May 10, 2007
  3. SomervillePrius

    SomervillePrius New Member

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    It's been discussed many times before.

    Unfortunately the 99.9MPG is just a limit on the screen. The actual calculation for average MPG is much more accurate. So it it says 50.2 you are getting about 50.2 miles/gallon

    The on screen calculation is actually slightly positive (most of the time) compared to measuring miles driven with gas filled. People who have tracked it manually over time only see small difference and most with the screen read-out being slightly positive.
     
    #3 SomervillePrius, May 10, 2007
  4. adgo82

    adgo82 New Member

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    <div class='quotetop'>QUOTE(SomervillePrius @ May 10 2007, 06:19 AM) [snapback]438952[/snapback]</div>
    With the bladder I find the actual calculation to be highly inaccurate.
     
    #4 adgo82, May 10, 2007
  5. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    In the early days, there were some auto reviewers who criticized the way the screen shows "99.9" because they thought it was confusing. What would have been more confusing is if the screen were accurate in its display and showed "∞"

    As stated above, the bladder can hold more or less gas depending on air temperature when refilling. For this reason, manual calculations are not always accurate.

    However, the Prius knows exactly when it's squirting gasoline into a cylinder. It knows exactly how much gasoline it's squirting per cycle. Of course it knows exactly how far it's rolled. So asking a computer to compute the amount of gasoline squirted into the pistons over a given distance is many times more accurate than attempting manual calculations and has nothing to do with what is displayed on the MFD to appease the humans.
     
    #5 TonyPSchaefer, May 10, 2007
  6. AndreJ

    AndreJ New Member

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    Thank you for the answer guys, i guess ill have to take your word for it. Im just skeptical because i have seen links and videos like http://www.youtube.com/watch?v=51nMDhu7qIE (shows pic at 1:40 ) that show prius's that have those battery kits in them with the energy monitor showing 99.9, so wouldnt that mean that the computer is only able to calculate an average mpg to the nearest 99.9 MPG? it makes sense to me but i geuss for a normal non modified prius it works out? i geuss the best thing to do would be to just test this out on my own eh? :rolleyes:
     
    #6 AndreJ, May 10, 2007
  7. bredekamp

    bredekamp Member

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    <div class='quotetop'>QUOTE(AndreJ @ May 10 2007, 03:23 PM) [snapback]438998[/snapback]</div>
    Mine just shows 0. Then again that's litres/100km. :p
     
    #7 bredekamp, May 10, 2007
  8. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(AndreJ @ May 10 2007, 06:23 AM) [snapback]438998[/snapback]</div>
    Nope. It only means that the display only handles 0 to 99.9. If you use CAN-View it displays up to 255. That's the largest decimal equivalent of a 2 digit hex value. They just don't want to add to the confusion by displaying infinity as the mileage when you're moving without using gas. The computer calculates mileage over an extended distance by keeping track of total miles traveled and total gas consumed. It doesn't do an average of what's shown on the display. For any given tank, it's much more accurate (or at least more consistent) than any calculations made by dividing miles traveled by gallons pumped into the tank.

    Dave M.
     
    #8 dmckinstry, May 10, 2007
  9. daniel

    daniel Cat Lovers Against the Bomb

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    <div class='quotetop'>QUOTE(AndreJ @ May 10 2007, 06:23 AM) [snapback]438998[/snapback]</div>
    The computer knows the real number. The screen shows a truncated number with an upper limit because the LEDs for instantaneous mileage only have three digits. Do not make the mistake of equating the display with the computer. The limitations of the display do not affect the computer.
     
    #9 daniel, May 10, 2007
  10. Rangerdavid

    Rangerdavid Senior Member

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    Yeah, and now with my ScanGauge II when I'm in the glide portion of a P&G, it reads "9999.99" - but that's not confusing because it doesn't go another digit. Its just using not gas, as it shows no RPMs. However, there are times its getting 250 or 300 MPG or any three digit number because there are still some RPMs going on and the MFD will show 99.9.

    All in all, the MFD after months, years, or 15-20,000 miles will average out to be very accurate.
     
    #10 Rangerdavid, May 10, 2007
  11. Tempus

    Tempus Senior Member

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    <div class='quotetop'>QUOTE(AndreJ @ May 10 2007, 09:23 AM) [snapback]438998[/snapback]</div>
    Generally, when working with computers, a display limitation is not a calculation limitation.

    Just because you set your Excel Spreadsheet to display one decimal point of data doesn't mean that the computer isn't keeping track of much more behind the screen.
     
    #11 Tempus, May 10, 2007
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