Scanguage II fuel consumption calibration for E0 fuel

Discussion in 'Gen 3 Prius Fuel Economy' started by Robert Holt, Aug 5, 2016.

  1. Robert Holt

    Robert Holt Senior Member

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    I have consistently used non-ethanol "E0" gasoline this summer and run several tankfuls down to the beep and flashing-last-pip before refueling (500-600 miles). At each refueling I reset the correction factor used by the Scangauge to estimate fuel consumption based on the fuel-injector information coming from the Prius's ECU. The Scanguage correction factor that works most accurately for E0 fuel is 6.3%. Based on previous experience with 10% ethanol E10 fuel, the Scanguage correction factor for that fuel is more like 10-12%. Do these correction factors agree with other Scanguage users?
    Under the "trips" menu in the Scanguage II is a "tank to empty" parameter, which I have checked at exactly the time I get the beep and flashing-last-pip low fuel warning. With the E0 fuel and a correction factor of 6.3%, the "tank to empty" estimate at time of beep is 2.5-2.6 gallons, which is noticeably higher than Bob Wilsons's estimate of 2.1 gallons using E10 fuel when run to empty. Has anyone else used either the Scanguage "tank to empty " approach or Bob Wilson's fuel exhaustion approach to estimate actual fuel remaining for E0 fuel at the time of the low-fuel warning beep?
    Trying to get the Scangauge fuel consumption accurately calibrated so thanks in advance for your help!
     
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  2. CR94

    CR94 Senior Member

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    My Scangauge shows 0.02 GPH consumption rate when it is actually zero, with engine stopped, with car stopped or coasting at less than about 45mph. It sometimes incorrectly shows around 0.33 GPH when the engine is being turned by the wheels while coasting at more than about 45 mph. In the latter circumstance, at other seemingly random times it (correctly) shows 0.00 GPH. Why? The MPG numbers it shows are affected correspondingly, MPG being equal to MPH/GPH.

    IF the ScanGauge uses the false ~0.33 GPH consumption rate integrated over time to compute fuel consumed for calibration purposes, the calibration will be way out of whack. That said, my apparent correction factor is around 12% on E10. It seems inconsistent, possibly because of the 0.33 GPH problem. (The 0.02 GPH issue would throw off the calibration too, to a smaller extent.)

    The only way I can confirm the engine is not actually consuming fuel during higher speed coasting is to note that the coolant temperature drops at about the same rate whether ~0.33 GPH or 0.00 GPH is displayed.
     
  3. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Actually the 2.1 gallons after flash works for the car sitting in my driveway. I would expect that other Gen-3 Prius tested the same way would have a different results:
    1. When flash begins:
      1. reset a trip meter
      2. put exactly 1 gallon measured, spare gas can in the car
      3. drive routes where you can coast to a safe shoulder when the engine runs out
    2. When car runs out of gas:
      1. add 1 gallon
      2. take photos of all trip meters
    3. Drive directly to nearest gas station and fill up
    4. Do the math and share with the community
    Bob Wilson
     
  4. Redpoint5

    Redpoint5 Senior Member

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    This seems like a cumbersome way to determine correction factor. Why not hand calculate MPG and compare it to what the SG thinks it is, then input the correction factor?
     
  5. CR94

    CR94 Senior Member

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    Yes, and more cumbersome than the method ScanGauge's instructions recommend, by an even wider margin. That is to compare fuel burned between fill-ups according to the pumps to fuel burned over the same interval in the ScanGauge's estimation, and correct accordingly. The trick to getting a stable number is to do it over a long enough interval that fill inconsistencies are diluted, and make only small adjustments.
     
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  6. Robert Holt

    Robert Holt Senior Member

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    Yes. My E0 estimates of the correction percentage were slight over and under estimates, so I used a "split the difference" heuristic and arrived at the 6.3% correction, which has been accurate to within 0.1 gallons on the last 3 refueling stops. Now to use it.
     
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