Spectrum 3.0L GM, Parts & Service Manual

Page: 24 / 327

24
engines rotational position. The crank sensor is the
source of all other ECU functions if this sensor is
not functioning the ECU will not see an engine
speed and will not provide fuel or spark to the en-
gine.
Fuel Rail Assembly and LPG Injectors.
The gaseous LPG flows into the fuel rail where it is
distributed to the four LPG injectors. At the oppo-
site end of the fuel rail to the inlet port there is a
Fuel Absolute Pressure (FAP) sensor (also known
as a Fuel Rail Pressure Sensor) this sensor allows
the ECU to lengthen or shorten the fuel injector
pulse width to compensate for variations in the ab-
solute fuel pressure supplied to the injectors. This
injector assembly has one end inserted into the
manifold ports and the other end inserted into the
fuel rail ports. There is an o-ring seal on the mani-
fold side and an o-ring and split spacer seal on the
fuel rail side. The fuel rail holds the injectors in
place.
A Spectrum IV Gaseous Fuel Injector
The 2011 saturated drive injectors operate on a two
stage, pilot actuated principal. When the coil is ac-
tuated it pulls the primary seal off the primary orifice
against the force of the flat return spring. This al-
lows gas to flow out of the upper chamber of the
injector. Because the orifice supplying the upper
chamber is smaller than the primary orifice which is
now allowing fuel to flow out of the upper chamber,
the pressure drops in this chamber and the now
higher pressure in the lower chamber pushes the
main secondary seal off the secondary orifice and
allows full flow of the injector (this occurs in about 1
to 2 ms). When the coil is de-energized the primary
seal is returned to cover the primary orifice by the
force of the flat spring and pressure builds in the
upper chamber forcing the secondary seal down to
seal the secondary orifice and shutting off all flow of
gas.