Service manual

G420F(FE) Service Manual Chapter 5. Engine Management System (EMS) 160
G420FE 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 Dual Fuel System for G420FE Engine on Certified Systems
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 Hall Effect 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.