**As I understand it (please note, I am not speaking from any real
authority here) no injector is perfect. Some are clogged a little. Some
are clogged a lot. Some are not clogged at all. Pumps are subject to wear.
As a consequence, the BEST way to measure actual fuel consumption, is to
measure the amount of fuel used, rather than inferring how much fuel
SHOULD be going into the cylinders.

Having said all that: My present car probably uses pulse measurement
techniques and the computer appears to be respectably accurate (though
I've never actually checked it).


All injectors should be within 5% of rated flow, or engine performance and
fuel economy will suffer. When new, they're within a percent or so, and
usually hold up pretty well. Measuring the pulsewidth should in most cases
be at least as accurate as typical flow sensors.