Kohler command pro ECH749 Service Manual page 60

EFI SYSTEM-BOSCH
Typical electronic fuel injection (EFI) system and related
components include:
● Fuel tank and valve.
● Fuel pump.
● Fuel fi lter.
● Fuel rail.
● Fuel line(s).
● Fuel injectors.
● Fuel pressure regulator.
● Throttle body/intake manifold.
● Electronic control unit (ECU).
● Ignition coils.
● Engine (oil) temperature sensor.
● Throttle position sensor (TPS).
● Speed sensor.
● Crankshaft position sensor.
● Oxygen sensor.
● Wire harness assembly & affi liated wiring.
● Malfunction indicator light (MIL).
● Intake air temperature sensor.
FUEL RECOMMENDATIONS
Refer to Maintenance.
FUEL LINE
Low permeation fuel line must be installed on all Kohler
Co. engines to maintain EPA and CARB regulatory
compliance.
Operation
NOTE: When performing voltage or continuity tests,
avoid putting excessive pressure on or against
connector pins. Flat pin probes are
recommended for testing to avoid spreading or
bending terminals.
EFI system is designed to provide peak engine
performance with optimum fuel effi ciency and lowest
possible emissions. Ignition and injection functions
are electronically controlled, monitored and continually
corrected during operation to maintain ideal air/fuel ratio.
Central component of system is Engine Control Unit
(ECU) which manages system operation, determining
best combination of fuel mixture and ignition timing for
current operating conditions.
An electric fuel pump is used to move fuel from tank
through fuel line and in-line fuel fi lter. A fuel pressure
regulator maintains a system operating pressure of
39 psi and returns any excess fuel to tank. At engine,
fuel is fed through fuel rail and into injectors, which
inject it into intake ports. ECU controls amount of fuel
by varying length of time that injectors are "ON." This
can range from 1.5-8.0 milliseconds depending on fuel
requirements. Controlled injection of fuel occurs each
crankshaft revolution, or twice for each 4-stroke cycle.
One-half total amount of fuel needed for one fi ring of a
cylinder is injected during each injection. When intake
valve opens, fuel/air mixture is drawn into combustion
chamber, ignited, and burned.
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ECU controls amount of fuel being injected and ignition
timing by monitoring primary sensor signals for engine
temperature, speed (RPM), and throttle position (load).
These primary signals are compared to preprogrammed
maps in ECU computer chip, and ECU adjusts fuel
delivery to match mapped values. After engine reaches
operating temperature, an exhaust gas oxygen sensor
provides feedback to ECU based upon amount of
unused oxygen in exhaust, indicating whether fuel
mixture being delivered is rich or lean. Based upon this
feedback, ECU further adjusts fuel input to re-establish
ideal air/fuel ratio. This operating mode is referred to as
closed loop operation. EFI system operates closed loop
when all three of following conditions are met:
● Oil temperature is greater than 35°C (95°F).
● Oxygen sensor has warmed suffi ciently to provide a
signal (minimum 375°C, 709°F).
● Engine operation is at a steady state (not starting,
warming up, accelerating, etc.).
During closed loop operation ECU has 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
ideal air/fuel ratio. This system requires a minimum
engine oil temperature greater than 80°C (176°F) to
properly adapt. These adaptive values are maintained as
long as ECU is not reset.
During certain operating periods such as cold starts,
warm up, acceleration, etc., an air/fuel ratio richer than
14.7:1 is required and system operates in an "open loop"
mode. In "open loop" operation oxygen sensor output
is not used, and controlling adjustments are based on
primary sensor signals and programmed maps only.
System operates "open loop" whenever three conditions
for closed loop operation (above) are not being met.
ECU is a brain or central processing computer of
entire EFI fuel/ignition management system. During
operation, sensors continuously gather data which
is relayed through wiring harness to input circuits
within ECU. Signals to ECU include: ignition (on/off),
crankshaft position and speed (RPM), throttle position,
oil temperature, exhaust oxygen levels, and battery
voltage. ECU compares input signals to programmed
maps in its memory to determine appropriate fuel and
spark requirements for immediate operating conditions.
ECU then sends output signals to set injector duration
and ignition timing.
ECU compares input signals to programmed maps in
its memory to determine appropriate fuel and spark
requirements for immediate operating conditions. ECU
then sends output signals to set injector duration and
ignition timing.
ECU continually performs a diagnostic check of itself,
each of sensors, and system performance. If a fault
is detected, ECU can turn on a Malfunction Indicator
Light (MIL) (if equipped) on equipment control panel,
store fault code in its fault memory, and go into a default
operating mode. Depending on signifi cance or severity
of fault, normal operation may continue. A technician can
access stored fault code using a blink code diagnosis
fl ashed out through MIL. An optional computer software
diagnostic program is also available, refer to Tools and
Aids.
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