Roman,

Most of the EFI port injection engines (as opposed to "throttle body" type
with a central injector) do vary the fuel pressure based on engine load
(manifold vacuum).  A vacuum signal from the intake manifold is applied to
the fuel pressure regulator diaphragm so the fuel pressure tracks with
manifold vacuum.  This causes the pressure differential across the injector
nozzle to be constant regardless of manifold vacuum.  That way, injector
fuel flow per unit of time is constant for any manifold vacuum.  This
approach makes it much easier for the engine control module (ECM) to
calculate correct fuel delivery since manifold vacuum need not be measured
and factored in.

Some newer systems are now using constant fuel pressure, and requiring the
ECM to compensate the injector pulse width for the variation in intake
manifold vacuum.

Before trying to relate injector duration to fuel consumption it would be
very important to know which system was on the vehicle.

Randy
www.glitchbuster.com


> The fuel injector system runs at a regulated
> pressure and the mechanical regulator works quite
> well. Pressure deviation is close to nonexistant
> as the system is designed to have sufficient overhead,
> which is the easiest way to control fuel as only
> injector duration needs to be considered. So YES
> measuring speed, revs and injector duration should
> give a very accurate fuel economy reading. :o)
> -Roman

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