Injector supply voltage & positioning.

[Bohdan L Bodnar]

There are two types of fuel injectors in use:  saturated switch driven and
peak-and-hold.

Saturated switch injectors are either high-impedance (about 16 ohms dc) or low
impedance (about 3 ohms dc).  Peak-and-hold injectors are low impedance.  Low
impedance saturated switch injectors are always driven via resistance wire so
as to limit current.

Peak-and-hold injectors typically are driven at full supply voltage (less
voltage drop across driving transistor) for a short time (e.g., in GM's
throttle body systems, this time is 1.5 ms) and then power is drastically cut.
The idea behind peak-and-hold injectors is the same as in pull-in and hold-in
windings on starter solenoids:  it takes more power to overcome static
friction than to overcome dynamic friction.  If one 'scopes a peak-and-hold
injector, one will see two distinct back-emf "kicks" across the injector.
I've never seen peak-and-hold injectors used for anything other than TBI
systems.

Saturated switch injectors are merely driven via a saturated switch ("class C
amplifier" for you EE types) -- either a power MOSFET or an NPN switching
transistor.

Hope this helps...

Regards,

Bohdan Bodnar