On Fri, 26 Sep 1997 13:22:14 -0800 Andrew Warren <fastfwd@IX.NETCOM.COM>
writes:
>
>I mean, think about it... If YOU were designing a fuel-consumption
>display for a fuel-injected car, would you get the information by
>installing two expensive flow-meters, measuring flow to the
>injectors and subtracting the flow back FROM the injectors, or would
>you go for the software-only method of simply accumulating the widths
>of the injector pulses and multiplying that by the known flow rate of
>each injector?
>
This is based on the assumption that the injectors are designed and built
to inject a known amount of fuel for a certain pulse width.  Which they
are.  The fuel pressure reaching the injectors is regulated by a
mechanical regulator and maybe double-checked by a sensor.  Other than
that, the connection from the computer's table of fuel delivery for
various operating conditions and the actual delivery of fuel is open
loop.  Some overall adjustment can be made from sensors like the exhaust
oxygen sensor.  When running properly, some oxygen leaves the engine
unburned.  If there is an excess of fuel the oxygen concentration will
drop, and fuel and CO leave unburned instead.  This is pollution.  Likely
this compensation is only done at idle, since most pollution tests are
only done at idle.

If you are trying to look for injector trouble by comparing the amount of
fuel the computer thinks it's allowing into the engine and the amount
that actually does go into the engine, a fuel flow sensor would be
required.  A good one for that would be the one on the gas pump when
refilling the tank.  It sould agree with the pulse-integrator "gallons
used".