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Display screen and fuel gauge calibration?

Discussion in 'Generation 1 Prius Discussion' started by SteamRollerCC, Dec 27, 2012.

  1. SteamRollerCC

    SteamRollerCC Junior Member

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    2002 Prius
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    I've been noticing that the MPG calculation and chart has been a bit off when I drive... so then I begin manually calculating the MPG with how many miles I drive and gallons of gas and I get diferences like 50.8mpg vs screen saying 54.2 for the same miles driven. So I begin thinking that might be normal for the screen display...

    Then another thing that I noticed that got my attention more is that the fuel garage started blinking to add more fuel when I consumed 10 gallons (which makes sense for an 11.9 gallon tank). Another time it started blinking, it only consumed 8.5 gallons.

    Anybody know what might be wrong with these miscalibrations? Or am I just bring too frustrated...?
     
    #1 SteamRollerCC, Dec 27, 2012
  2. bwilson4web

    bwilson4web BMW i3 and Model 3

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    You need to check the calibration of your trip meter distance with a known route. Many highways have mile markers. So take a 10+ mile drive and reset the trip meter when you pass a mile marker. Then drive for 10 miles and compare the trip meter reading offset with the mile marker. You'll also find your speedometer is off too.

    What happens is the original tire was rated at ~902 revolutions per mile. But after market tires come in different sizes and diameters. If your tire is on the 'higher revs per mile' and are worn down, it will look like you are holding say 50 mph but in reality you might be going 2% slower, or 49 mph. I've deliberately gone the other way.

    I am running the largest diameter, 14" tires that fit in the wheel well (the rear are smaller than the front.) My tires, Sumitomo T4 P185/70R14, turn 867 revs/mile, about 6% slower. So my speedometer always read lower than true speed and the tripmeter is off too. However, I have in effect added an 'over drive' to my NHW11 so my mileage is slightly better. It also improves straight-line stability, the car is less 'twitchy' or 'neutral stability.'

    Our NHW11s also have a bladder lined, fuel tank. Depending upon pure, random chance, you may or may not get a full tank of gas (possibly a bubble between the bladder and tank?) Regardless, the most I've ever put in is about 11.8 gallons but then I am used to having a 1 gallon, spare can in the trunk when I'm doing gasoline quality experiments.

    So let me suggest checking the trip meter against a known standard distance (or GPS) and then adjust everything else as is appropriate. I know of no known 'calibration adjustment' other than pen-and-paper.

    GOOD LUCK!
    Bob Wilson
     
    #2 bwilson4web, Dec 27, 2012
  3. SteamRollerCC

    SteamRollerCC Junior Member

    Joined:
    Aug 26, 2012
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    Vehicle:
    2002 Prius
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    I've done some more tests and this behavior keeps getting odd with the battery/MPG. I have a brand new battery in my 2002 Prius, and when I barely evn use it, it goes to 50% and the engine begins turning on like crazy. The other day I drove it about 200 miles and went to fill up gas... it only filled up 2 gallons and read it as full! Then I drive it and after 30 miles... 2 bars fall of quick.

    Is there some part that's controlling ths that needs to be looked it? I'm sure the battery's fine, but could this be the ECU?
     
    #3 SteamRollerCC, Jan 29, 2013
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