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post #2 of (permalink) Old 26th July 2012
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Re: Fuel gauge telling lies? Megane Coupe III - 59 plate.

I wouldn't say the onboard mpg computer is a liar but it is economical with the truth.
The system cannot measure actual flow rates of fuel but extrapulates from data supplied by thye ECU . It measures time, distance, fuel settings, engine rpm, engine load, etc. Therefore the computer is using purely historical data. For instance say you had completed a long run and averaging 50 mpg. Then you stop the car. When you start the engine without moving the ECU will record fuel has been used yet the car has travelled no distance. The computer will then re-calculate the average of the previous readings and the most recent readings - hence the apparent big drop in mpg and calculated range.
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