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Discussion Starter #1 (Edited)
Just did a trip that ran tank to zero range. Computer said 28.6 mpg (was 31.5 on highway) filled up stuffed just like I did yesterday and I calculated 24.4mpg. It isn't even close. I bet when they set range based on 13 gallons the dummies also let everything else calc off that rate. We'll need that issue reprogrammed at some point I don't mind 1 mpg but 4+ is pretty bad.
 

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Just did a trip that ran tank to zero range. Compter said 28.6 mpg (was 31.5 on highway) fiulled up stuffed just like I did yesterday and I calculated 24.4mpg. It isn't even close. I bet when they set range based on 13 gallons the dummies also let everything else calc off that rate. We'll need that issue reprogrammed at some point I don't mind 1 mpg but 4+ is pretty bad.
I have found my trip computer to be very close, to what I calculate after a fill up. May be a 5% difference between the two.
Ron
 

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Mine is way off, but reality is always better than the computer...
 

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Mine is off by more than that. My calculated mpg is consistently 6-7 over the computer display.
 

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Typically the fuel economy is calculated by the ECU by integrating the injector duration less dead time over time and using a lookup table to calculate volume. Distance might be speed integrated or sensor pulses counted.
Because the integration may occur slower than each cylinder firing there can be inaccuracy in transient events, but this is going to be small.
The minor variables which are not compensated are fuel temperature, fuel pressure and injector voltage.
The major variables which will affect things are the distance calculation (tire size, pressure) and fuel energy density.
I wonder if Lotus re-calibrated the ECU for US gasoline vs UK petrol? I also wonder how much difference there is state to state in ethanol content.
 

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Discussion Starter #9
All other vehicles I own are within 1mpg. They definitely didn't recalculate something. I was amazed at the mileage up until yesterday.
 
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