Kohler ECV940 Service Manual page 28

EFI SYSTEM-ELECTRONIC THROTTLE BODY (ETB)
ECU is brain or central processing computer of entire
EFI and ETB/electronic governor 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, requested
customer speed input, oil temperature, intake air
temperature, exhaust oxygen levels, manifold absolute
pressure, 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, ignition
timing, and ETB throttle opening.
ECU continually performs a diagnostic check of itself,
each sensor, 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 or use KOHLER
System (KDS) Gen 2, see Tools and Aids.
ECU requires a minimum of 6.0 volts to operate.
To prevent engine over-speed and possible failure, a
rev-limiting feature is programmed into ECU. If maximum
RPM limit (4500) is exceeded, ECU suppresses injection
signals, cutting off fuel fl ow. This process repeats itself in
rapid succession, limiting operation to preset maximum.
Wiring harness used in EFI system connects electrical
components, providing current and ground paths for
system to operate. All input and output signaling occurs
through two special all weather connectors that attach
and lock to ECU. Connectors are Black and Grey and
keyed diff erently to prevent being attached to ECU
incorrectly.
Condition of wiring, connectors, and terminal
connections is essential to system function and
performance. Corrosion, moisture, and poor connections
are as likely cause of operating problems and system
errors as an actual component. Refer to Electrical
System for additional information.
EFI system is a 12 VDC negative ground system,
designed to operate down to a minimum of 6.0 volts.
If system voltage drops below this level, operation
of voltage sensitive components such as ECU, fuel
pump, ignition coils, and injectors will be intermittent
or disrupted, causing erratic operation or hard starting.
A fully charged, 12 volt battery with a minimum of 350
cold cranking amps is important in maintaining steady
and reliable system operation. Battery condition and
state of charge should always be checked fi rst when
troubleshooting an operational problem.
Keep in mind that EFI-related problems are often caused
by wiring harness or connections. Even small amounts
of corrosion or oxidation on terminals can interfere with
milliamp currents used in system operation.
Cleaning connectors and grounds will solve problems
in many cases. In an emergency situation, simply
disconnecting and reconnecting connectors may clean
up contacts enough to restore operation, at least
temporarily.
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If a fault code indicates a problem with an electrical
component, disconnect ECU connector and test for
continuity between component connector terminals and
corresponding terminals in ECU connector using an
ohmmeter. Little or no resistance should be measured,
indicating that wiring of that particular circuit is OK.
Crankshaft position sensor is essential to engine
operation; constantly monitoring rotation and speed
(RPM) of crankshaft. There are 23 consecutive teeth
cast into fl ywheel. One tooth is missing and is used to
reference crankshaft position for ECU.
During rotation, an AC voltage pulse is created within
sensor for each passing tooth. ECU calculates engine
speed from time interval between consecutive pulses.
Gap from missing tooth creates an interrupted input
signal, corresponding to specifi c crankshaft position near
BDC for cylinder #1. This signal serves as a reference
for control of ignition timing by ECU. Synchronization of
inductive speed pickup and crankshaft position takes
place during fi rst two revolutions each time engine is
started. Sensor must be properly connected at all times.
If sensor becomes disconnected for any reason, engine
Diagnostic will quit running.
®
Throttle position sensor (TPS) is used to indicate throttle
plate angle to ECU. Since throttle (by way of governor
or customer speed input/ETB throttle opening) reacts to
engine load, angle of throttle plate is directly related to
load on engine.
TPS is sealed and not serviced separately. Mounted on
electronic throttle body and operated directly off end of
throttle shaft, TPS works as a potentiometer, varying
voltage signal to ECU in direct correlation to angle
of throttle plate. This signal, along with other sensor
signals, is processed by ECU and compared to internal
preprogrammed maps to determine required fuel and
ignition settings for amount of load.
TPS auto-learn is an automated process. No adjustment
is required.
Engine temperature sensor is used by system to
help determine fuel requirements for starting (a cold
engine needs more fuel than one at or near operating
temperature).
Mounted in crankcase next to breather cover, it has
a temperature-sensitive resistor that extends into oil
fl ow. Resistance changes with oil temperature, altering
voltage sent to ECU. Using a table stored in its memory,
ECU correlates voltage drop to a specifi c temperature.
Using fuel delivery maps, ECU then knows how much
fuel is required for starting at that temperature.
Temperature/Manifold Absolute Pressure (TMAP) sensor
is an integrated sensor that checks both intake air
temperature and manifold absolute pressure.
Intake Air Temperature control is a thermally sensitive
resistor that exhibits a change in electrical resistance
with a change in its temperature. When sensor is cold,
resistance of sensor is high. As sensor warms up,
resistance drops and voltage signal increases. From
voltage signal, ECU can determine temperature of intake
air.
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