Isuzu C22NE Workshop Manual page 467

DRIVEABILITY AND EMISSIONS 6E1-297
STARTING MODE
When the ignition is first turned ON, the ECM energizes the
fuel pump relay for two seconds to allow the fuel pump to build
up pressure. The ECM then checks the engine coolant
temperature (ECT) sensor and the throttle position (TP) sensor
to determine the proper air/fuel ratio for starting.
The ECM controls the amount of fuel delivered in the starting
mode by adjusting how long the fuel injectors are energized by
pulsing the injectors for very short times.
THROTTLE BODY UNIT
The throttle body has a throttle plate to control the amount of
air delivered to the engine. The TP sensor and IAC valve are
also mounted on the throttle body.
Vacuum ports located behind the throttle plate provide the
vacuum signals needed by various components. Engine
coolant is directed through a coolant cavity in the throttle body
to warm the throttle valve and to prevent icing.
ELECTRONIC IGNITION SYSTEM
CRANKSHAFT POSITION (CKP)
SENSOR
The crankshaft position (CKP) sensor provides a signal used
by the engine control module (ECM) to calculate the ignition
sequence. The sensor initiates the 58X reference pulses which
the ECM uses to calculate RPM and crankshaft position. Refer
to Electronic Ignition System for additional information.
ELECTRONIC IGNITION
The electronic ignition system controls fuel combustion by
providing a spark to ignite the compressed air/fuel mixture at
the correct time. The provide optimum engine performance,
fuel economy, and control of exhaust emissions, the ECM
controls the spark advance of the ignition system. Electronic
ignition has the following advantages over a mechanical
distributor system:
• No moving parts.
• Less maintenance.
• Remote mounting capability.
• No mechanical load on the engine.
• More coil cool down time between firing events.
• Elimination of mechanical timing adjustments.
• Increased available ignition coil saturation time.