6.13 - Trip Computer (early models) ( Pete Crosby,  December 4, 2001 )

Don't give that little computer and the Jag engineers too much credit with regard to range.

It seems that the range shown is based strictly upon the amount of fuel the computer thinks is in the tank (based upon the level and NOT based upon fuel usage calculated from injector "on" time) and the currently calculated average fuel economy (which IS calculated based upon miles traveled and injector "on" time). Hint: check your range after filling the car up but before you reset the computer. It will calculate the range based upon the current average MPG and the amount of fuel it decides is in the tank, as read from the level sensor.

Average speed is calculated from engine run time and distance traveled.

Fuel used is calculated from the amount of time the injectors are open (i.e. injector "on" time). This is why dirty injectors or a bad fuel
pressure regulator will cause the computer's calculation of fuel usage to be way off when compared to how much fuel it actuall takes to refill the tank.

Instant fuel economy is calculated using injector "on" time and distance traveled and is recalculated about every 5 seconds.