Efi Fuel System Components; Operation - Kohler COMMAND CH18 Service Manual

Gasoline/Alcohol blends
Gasohol (up to 10% ethyl alcohol, 90% unleaded
gasoline by volume) is approved as a fuel for Kohler
EFI engines. Other gasoline/alcohol blends are not
approved.
Gasoline/Ether blends
Methyl Tertiary Butyl Ether (MTBE) and unleaded
gasoline blends (up to a maximum of 15% MTBE by
volume) are approved as a fuel for Kohler EFI engines.
Other gasoline/ether blends are not approved.

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
• Fuel Filter
• Fuel Rail
• Fuel Line(s)
• Fuel Pressure Regulator
• Fuel Injectors
• Throttle Body/Intake Manifold
• Engine Control Unit (ECU)
• Ignition Coils
• Engine (Oil) Temperature Sensor
• Throttle Position Sensor (TPS)
• Speed Sensor
• Oxygen Sensor
• Wire Harness Assembly & Affiliated Wiring,
• Malfunction Indicator Light (MIL)

Operation

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 the
theoretical ideal or "stoichiometric" air/fuel ratio of
14.7:1.
The central component of the system is the Motronic
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. A fuel
pressure regulator maintains a system operating
pressure of 39 psi and returns any excess fuel to the
tank. At the engine, fuel is fed through the fuel rail and
into the injectors, which inject it 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 injected and the
ignition timing by monitoring the primary sensor
signals for engine temperature, speed (RPM), and
throttle 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. An oxygen sensor
provides continual 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 reestablish 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 35°C (95°F).
b. The oxygen sensor has warmed sufficiently to
provide a signal (minimum 375°C, 709°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 of
14.7:1. The system requires a minimum engine oil
temperature greater than 55°C (130°F) to properly
adapt. These adaptive values are maintained as long as
the ECU is "powered up" by the battery.
™
During certain operating periods such as cold starts,
warm up, acceleration, etc., an air/fuel ratio richer than
14.7:1 is required and the system operates in an "open
loop" mode. In "open loop" operation the monitoring
of exhaust gases (output) is not used, 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.
Section 5B
EFI Fuel System
5B.3
5B