No, I can't claim it worked that well- but it sure was fun trying!
I didn't have the time to develop it so that it gave a sensible reading under all conditions.
I think there are too many variables to calibrate on this engine; massive variations in fuel pressure, the fuel temperature - varies a lot because of the high pumping pressures, so the density of fuel varies.
I always had a regular jump in injus every few seconds or so as well.
The replacement car has a mpg gauge!
Thanks for your help along the way, I plan to use the arduino hardware for an intelligent grilleblock and temperature indication system now...