Paul wrote:

Something sometimes overlooked when designing EFI is what happens
when the system voltage drops off.

At eight volts there are questions about the amount of fuel the
injectors will inject and the pressure from the fuel pump.

>From this it looks like a backup alternator is called for in
aircraft systems that are open loop.

Rodger Hilyard wrote:

On my electronic injector system, I have an active voltage regulator
that supplies 7.5 volts to the control circuit, a constant current
generator
that supplies sustaining current to the injector, and a charge capacitor
that supplies turn on drive to rapidly open the low impedance injector.

 I have tested the system from 16 VDC supply to 8.0 VDC with less
than 1% chainge in pulse width with voltage.   At 8 or 9 Volts, your
battery is already kaput.... : )

  The fuel pump maintains needed overpressure to the fuel manifold
pressure regulator down to 9 VDC @ 8 gph and I can manually increase
the pulse width if needed below that limit. Subaru EFI pump (30gph) and
Bosch low ( 1.2 ohm ) impedamce injector, 15 psig rail.

 Rodger

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