Aeon 350cc, Service Manual

Page: 105 / 192

ELECTRONIC FUEL INJECTION
5-105
EFI OPERATION OVERVIEW
The EFI system is designed to provide peak engine
performance with optimum fuel efficiency and lowest possible
emissions. The ignition and injection functions are
electronically controlled, monitored and continually corrected
during operation to maintain peak performance.
The central component of the system is the Engine Control
Unit (ECU), which manages system operation, determining the
best combination of fuel mixture and ignition timing for the
current operating conditions.
An electric fuel pump is used to move fuel from the tank
through the fuel line and in-line fuel filter. At the engine, fuel
is fed through the fuel rail and into the injectors, which inject
into the intake ports. The ECU controls the amount of fuel by
varying the length of time that the injectors are "on." This can
range from 1.5-8.0 milliseconds depending on fuel
requirements. The controlled injection of the fuel occurs each
crankshaft revolution, or twice for each 4-stroke cycle.
One-half the total amount of fuel needed for one firing of a
cylinder is injected during each injection. When the intake
valve opens, the fuel/air mixture is drawn into the combustion
chamber, ignited and burned.
The ECU controls the amount of fuel being injected and the
ignition timing by monitoring the primary sensor signals for air
temperature, barometric air pressure, engine temperature,
speed (RPM), and throttle position (load). These primary
signals are compared to the programming in the ECU
computer chip, and the ECU adjusts the fuel delivery and
ignition timing to match the values.
During operation the ECU has the ability to re-adjust
temporarily, providing compensation for changes in overall
engine condition and operating environment, so it will be able
to maintain the ideal air/fuel ratio.
During certain operating periods such as cold starts, warm up,
acceleration, etc., a richer air / fuel ratio is automatically
calculated by the ECU.
The ECU is the brain or central processing computer of the
entire EFI fuel/ignition management system. During operation,
sensors continuously gather data which is relayed through the
wiring harness to input circuits within the ECU. Signals to the
ECU include: ignition (on/off), crankshaft position and speed
(RPM), throttle position, engine coolant temperature, air
temperature, and intake manifold air pressure and battery
voltage.
The ECU compares the input signals to the programmed maps
in its memory and determines the appropriate fuel and spark
requirements for the immediate operating conditions. The ECU
then sends output signals to set the injector duration and
ignition timing.
During operation, the ECU continually performs a diagnostic
check of itself, each of the sensors, and system performance. If
a fault is detected, the ECU turns on the “Check Engine” light
in the speedometer and stores the fault code in its fault
memory. Depending on the significance or severity of the
fault, normal operation may continue, or "Fail-Safe" operation
(slowed speed, richer running) may be initiated. A technician
can determine the cause of the “Check Engine” light by
initiating the “Blink Code” sequence or by using
Digital EFI
Diagnostic Software.
INTAKE AIR TEMPERATURE