Owner`s manual

SEQUENTIAL MULTIPORT
FUEL INJECTION SYSTEM
Your INFINITI engine uses a separate fuel
injector for each cylinder. These are placed
into the intake ports, so that they can spray
atomized fuel under pressure into the intake
air stream. These injectors are controlled
‘‘sequentially’’, which means that they operate
in each cylinder according to the firing order.
Each injector opens to spray its carefully
metered amount of fuel just before the intake
valve of the cylinder opens.
Constant Pressure
Fuel injector operation depends upon a supply
of fuel that is always maintained at a constant
pressure in relation to the pressure in the
engine intake manifold. Under pressure, the
fuel travels through the line, through a large
and efficient fuel filter mounted under the
hood, and into a ‘‘fuel rail’’ which feeds the
injectors. Fuel flows into the bases of the
injectors, where it is available to flow out of
the injector nozzles and into the intake ports
when the injectors are opened electrically by
signals from the ECM.
By allowing more or less fuel to return to the
tank, the fuel pressure regulator maintains the
pressure at the injectors at 34 psi (2.4 kg/cm
2
,
235 kPa) above manifold pressure.
That allows the ECM to adjust the flow of fuel
into the engine simply by controlling the
amount of time the injectors stay open. The
longer the injectors are held open, in milli-
seconds, the more fuel flow.
IGNITION TIMING CONTROL
For best efficiency, ignition timing must be
dynamic, that is it must change depending
upon the engine operating conditions. It must
respond to engine load, RPM changes, engine
temperature changes, altitude, and so on. For
precisely correct, automatic, adjustments in
ignition timing to take place, the ECM must
have sensors that tell about such conditions.
The most important of these is the crank angle
sensor. The camshaft position sensor tells the
ECM the engine speed and the positions of
the pistons under all conditions.
CONTROL OF COMBUSTION
TEMPERATURE
Oxides of nitrogen, in a number of chemical
variations, are among the major components
of photochemical air pollution. These nitrogen
oxide compounds are formed in the engine
when the combustion temperatures are higher
than about 2,000°F (1,093°C). One way to
decrease nitrogen oxide formation in the
engine, then, is to cool the temperature of
combustion slightly. This is done by allowing
a small amount of burned, and therefore inert,
exhaust gases to recirculate back into the
engine intake manifold where they can be
drawn into the cylinders.
TECHNICAL AND CONSUMER INFORMATION
9-5
Z 96.12.20/ X