Engine Speed Sensor - Kohler COMMAND CH18 Service Manual

Three different styles of ECU's have been utilized in EFI
production. The first style is easily identified by its
metal case with large 35 pin connector block, and also
as MA 1.7. See Figure 5B-1. The second and third styles
have plastic cases, but are smaller in overall size. These
have either a 24 pin or 32 pin connector block and
identified as MSE 1.0 or MSE 1.1 respectively. See
Figures 5B-2 and 5B-3. Basic function and operating
control remains the same between the three, however,
due to differences in the internal circuitry as well as
the wiring harness, none of the ECU's are
interchangeable. Certain individual service/
troubleshooting procedures also apply, where
applicable, they are covered individually as: "35 Pin"
(MA 1.7) Metal-Cased ECU, "24 Pin" (MSE 1.0) Plastic-
Cased ECU, or "32 Pin" (MSE 1.1) Plastic-Cased ECU.
General
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, oil temperature, exhaust oxygen
levels, and battery voltage. The ECU compares the
input signals to the programmed maps in its memory
to determine 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.
The ECU continually performs a diagnostic check of
itself, each of the sensors, and the system performance.
If a fault is detected, the ECU turns on the Malfunction
Indicator Light (MIL) on the equipment control panel,
stores the fault code in its fault memory, and goes into
a default operating mode. Depending on the
significance or severity of the fault, normal operation
may continue, or "limp home" operation (slowed
speed, richer running) may be initiated. A technician
can access the stored fault code using a "blink code"
diagnosis flashed out through the MIL. An optional
computer software diagnostic program is also
available, see Section 2.
The ECU requires a minimum of 7.0 volts to operate.
The adaptive memory in the ECU is operational the
moment the battery cables are connected, however the
adapted values are lost if the battery becomes
disconnected for any reason. The ECU will "relearn"
the adapted values if the engine is operated for 10-15
minutes at varying speeds and loads after the oil
temperature exceeds 55°C (130°F).
To prevent engine over-speed and possible failure, a
"rev-limiting" feature is programmed into the ECU. If
the maximum RPM limit (4125 RPM on MA 1.7, 4500
RPM on MSE 1.0 & MSE 1.1) is exceeded, the ECU
suppresses the injection signals, cutting off the fuel
flow. This process repeats itself in rapid succession,
limiting operation to the preset maximum.
Service
Never attempt to disassemble the ECU. It is sealed to
prevent damage to internal components. Warranty is
void if the case is opened or tampered with in any
way.
All operating and control functions within the ECU
are preset. No internal servicing or readjustment may
be performed. If a problem is encountered, and you
determine the ECU to be faulty, contact your source of
supply. Do not replace the ECU without factory
authorization.
The relationship between the ECU and the throttle
position sensor (TPS) is very critical to proper system
operation. If the TPS or ECU is changed, or the
mounting position of the TPS is altered, the applicable
"TPS Initialization Procedure" (see pages 5B.8 or 5B.9)
must be performed to restore the synchronization.

Engine Speed Sensor

Figure 5B-4. Engine Speed Sensor.
Section 5B
EFI Fuel System
5B.5
5B