Kohler Command PRO CH749, Руководство по обслуживанию

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5.3
Section 5
EFI Fuel System
5
EFI Fuel System Components
General
The Electronic Fuel Injection (EFI) system is a
complete engine fuel and ignition management
design. The system includes the following principal
components:
• Fuel Pump Module and Li ft Pump
• Fuel Filter
• High Pressure Fuel Line
• Fuel Line(s)
• Fuel Injectors
• Thro
tt le Body/Intake Manifold
• Electronic Control Unit (ECU)
• Ignition Coils
• Engine (Oil) Temperature Sensor
• Thro
tt le Position Sensor (TPS)
• Cranksha ft Position Sensor
• Oxygen Sensor
• Manifold Absolute Pressure Sensor (MAP)
• Wire Harness Assembly & A
ffi liated Wiring,
• Malfunction Indicator Light (MIL) - optional
• Intake Air Temperature Sensor
Operation
The EFI system is designed to provide peak engine
performance with optimum fuel e
ffi ciency and
lowest possible emissions. The ignition and injection
functions are electronically controlled, monitored and
continually corrected during operation to maintain the
ideal air/fuel ratio.
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.
A li ft fuel pump is used to move fuel from the tank
through an in-line fuel fi lter and fuel line. The fuel
is then pumped to the fuel pump module. The fuel
pump module regulates fuel pressure to a system
operating pressure of 39 psi. Fuel is delivered from the
fuel pump module through the high pressure fuel line
into the injectors, which inject the fuel 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 2 to over 12 milliseconds depending on
fuel requirements. The controlled injection of the fuel
occurs every other cranksha
ft revolution, or once for
each 4-stroke cycle. When the intake valve opens,
the air/fuel 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 engine temperature, speed (RPM),
and thro
tt le position (load). These primary signals
are compared to preprogrammed maps in the ECU
computer chip, and the ECU adjusts the fuel delivery
to match the mapped values. A
ft er the engine reaches
operating temperature, an exhaust gas oxygen sensor
provides feedback to the ECU based upon the amount
of unused oxygen in the exhaust, indicating whether
the fuel mixture being delivered is rich or lean. Based
upon this feedback, the ECU further adjusts fuel input
to re-establish the ideal air/fuel ratio. This operating
mode is referred to as closed loop operation. The EFI
system operates closed loop when all three of the
following conditions are met:
a. The oil temperature is greater than 60°C (140°F).
b. The oxygen sensor has warmed su ffi ciently to
provide a signal (minimum 400°C, 752°F).
c. Engine operation is at a steady state (not starting,
warming up, accelerating, etc.).
During closed loop operation the ECU has the ability
to readjust temporary and learned adaptive controls,
providing compensation for changes in overall engine
condition and operating environment, so it will be
able to maintain the ideal air/fuel ratio. The system
requires a minimum engine oil temperature greater
than 80°C (176°F) to properly adapt. These adaptive
values are maintained as long as the ECU is not reset.
During certain operating periods such as cold starts,
warm up, acceleration, high load, etc., a richer air/
fuel ratio is required and the system operates in an
open loop mode. In open loop operation the oxygen
sensor output is used to ensure engine is running
rich, and the controlling adjustments are based on the
primary sensor signals and programmed maps only.
The system operates open loop whenever the three
conditions for closed loop operation (above) are not
being met.
Important Service Notes!
• Cleanliness is essential and must be maintained
at all times when servicing or working on the EFI
system. Dirt, even in small quantities, can cause
signi
fi cant problems.
• Clean any joint or fi tt ing with parts cleaning
solvent before opening to prevent dirt from
entering the system.