[Diy_efi] : returnless fuel rails

[Greg Hermann]

At 7:00 PM 5/26/02, Perry Harrington wrote:
>FWIW...
>
>My understanding of these systems (used on ford explorer v8 and 99-up
>mustangs), is that they have an electronic fuel pressure gauge that feeds
>back to the computer.  The computer simply PWM controls the fuel pump to
>vary the voltage, and thus pressure/flow.
>
>It seems to me that it would be very trivial to make a circuit (or hack into
>the Megasquirt) that controls the fuel pump via feedback.
>
>The bonus on the Megasquirt is that since it's MAP based, you already know
>the intake manifold pressure and can use that to keep the pressure drop
>across the injectors linear.
>
>--Perry
>
All of the above sort closed loop control of fuel pressure can be
accomplished WITH a bypass, whether or not a regulator is used. A small
fixed orifice bypass AT THE HIGH POINT of the rails and other plumbing is
the ONLY real way to control vapor. (A float vent could also be used, but
WHY go for the extra moving parts?)

In fact, it isn't too hard to see using feedback control of fuel rail
pressure to a map (of engine load) being able to effectively double the
dynamic range of a given set of injectors, so long as fuel atomization
issues are dealt with adequately.

The dead end rails are STRICTLY an evaporative emissions measure, and NOT
necessarily the best approach for good fuel management/control under  high
performance conditions, so far as I can tell. One little bubble of vapor
into an injector at the wrong time IS more than enough to trigger a serious
detonation episode !

Greg



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