I recently discovered a little display option on my dash that gives
average mpg
current mpg (that one is depressing usually)
distance to empty
This is what comes from having a mobile computer for a car, I suppose. An old fashioned fuel gauge I could figure out and pretty much understood how it measured the contents of the tank.
So can someone explain in simple English, how all the new stuff is measured and calculated?
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I can't answer your question with any certainty but I can tell you that in my Focus the trip computer appears to be little more than a toy. Although the average fuel consumption indicates to 0.1 mpg the figure invariably changes in steps of 0.5 mpg. Also, if I add the distance to empty to the distance already travelled on that tankful (i.e. effectively the distance from full to empty) the figure will consistently change from over 500 miles immediately before filling up to just over 400 miles immediately after filling up!
--
L\'escargot by name, but not by nature.
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My Renault has the digital information plus a conventional dial to show how much fuel is left. But in reality I don't bother with the digital side, I know a full tank lasts 730 miles :-)
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Information required:
average mpg
current mpg (that one is depressing usually)
distance to empty
Actual infromation available:
1.Current speed. mph
2. Distance travelled (from last time trip was zeroed or appropriate button pushed)
3. Fuel used from (when ditto)
4. Current fuel tank reading.
So average mpg = 2/3
Current mpg = snapshot fuel being used (from ecu)/current speed
Distance to empty = 4/average mpg OR 4/current mpg.. (former most likely).
Notes: speedos overead by up to 10%
Fuel guages may under or overead at various points in the tank depending on its shape and the accuracy of the float height measurement.
Average mpg is a crude calculation.
So if the answer to any of the above question sis within 10-15% of reality, I would be very surprised..
madf
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Have just returned from 1000-mile trip to far north in wife's Clio 1.6 16v. Zeroed consumption just after leaving, and once more after about 750 miles - av.mpg had settled to 51.5 at that point, and settled to over 53 for the remainder of the trip. The fuel used was exactly 90 litres for the whole trip (within 20 miles as far as I can judge from the gauge). That makes 11 mpl, or 50 mpg, so the evidence (FWIW) is that the computer overestimates about in line with the odometer. The remarkable thing is that the handbook only claims 47mpg for 'inter-urban' consumption!
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