Hi valve-n-head, DirtyLude, ante, williB,
You're quite correct,
I had overlooked the 'excess return fuel line',
this of course means that fuel pump delivery is actually much
more than fuel consumption. Sorry about that.
I think this mention from DirtyLude actually nails it pretty well,
DirtyLude:
If you're thinking about an entirely passive solution, you can
pretty much forget about it. It would be real simple with a
microcontroller. Read the on time of the injector and average it
over the number of kilometres traveled,
taken from the speed sensor.
If i understand it right,
then the distance reference could come from a sensor on any
suitable part of the transmission, and the fuel reference could
come from the 'on time' of an injector.
I'm not sure at all how a microcontroller would be set up to give
fuel consumption, but programming one to do that would certainly
be easier than building some sort of calculating board of chips.
(a microcontroller is very similar to a computer, it can use
memory and do most things that a computer can do)
Best of luck with your project, John