Re: iPhone MPG calculator apps- Suggestions?
In theory the EVIC should be more accurate than any manual calculation. It measures the flow of fuel through the injectors (easy to calculate based on the duty cycle being called for by the ECM and the known flow rate of the injectors) and does a fairly simple calculation based on current speed. There's nothing magical about it and the only explanation I can see for differences would be the way it treats idling. In my rudimentary testing (reset the EVIC on fill up then compare my manual calculation to the displayed average on the next fill up) it's never off by more the 1% on any of the last few cars I've owned with this type of display, well within my manual calculation error.
Now, if you forget to reset the EVIC on every fill up then that's probably where you are getting your error from.
2012 Grand Cherokee SRT8 Black/Black