G643(E) Service Manual Chapter 5. Engine Management System (EMS) 148
G643E EMS (Engine Management System) Overview
General Description
MI-07 control system provides a complete, fully
integrated engine management system that meets
or exceeds 2007 emission standards for Large
Spark Ignited (LSI) engines established by the
California Air Resources Board (CARB) and the
Environmental Protection Agency (EPA).
The control system is applicable to naturally
aspirated engines running on LPG and/or gasoline.
It provides accurate, reliable, and durable control of
fuel, spark, and air over the service life of the engine
in the extreme operating environment found in
heavy-duty, under hood, on-engine electronic
controls.
MI-07 is a closed loop system utilizing a catalytic
muffler to reduce the emission level in the exhaust
gas. In order to obtain maximum effect from the
catalyst, an accurate control of the air fuel ratio is
required. A small engine control module (SECM)
uses two heated exhaust gas oxygen sensors
(HEGO) in the exhaust system to monitor exhaust
gas content. One HEGO is installed in front of the
catalytic muffler and one is installed after the
catalytic muffler.
[Figure 1] MI-07 LP Fuel System for G643E Engine
The SECM makes any necessary corrections to the
air fuel ratio by controlling the inlet fuel pressure to
the air/fuel mixer by modulating the dual fuel trim
valves (FTV) connected to the regulator. Reducing
the fuel pressure leans the air/fuel mixture and
increasing the fuel pressure enriches the air/fuel
mixture. To calculate any necessary corrections to
the air fuel ratio, the SECM uses a number of
different sensors to gain information about the
engine’s performance. Engine speed is monitored
by the SECM through a Variable reluctance (VR)
sensor. Intake manifold air temperature and
absolute pressure are monitored with a TMAP
sensor. MI-07 is a drive-by-wire (DBW) system
connecting the accelerator pedal to the electronic
throttle through the electrical harness; mechanical
cables are not used. A throttle position sensor (TPS)
monitors throttle position in relation to the
accelerator pedal position sensor (APP) command.
Even engine coolant temperature and adequate oil
pressure are monitored by the SECM. The SECM
controller has full adaptive learning capabilities,
allowing it to adapt control function as operating
conditions change. Factors such as ambient
temperature, fuel variations, ignition component
wear, clogged air filter, and other operating variables
are compensated.
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