G643(E) Service Manual
Chapter 5. Engine Management System (EMS)
168
G643 EMS (Engine Management
System) Overview
General Description
MI-04 control system provides a complete, fully
integrated engine management system for naturally
aspirated engines.
It provides accurate, reliable, and durable control of
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.
The SECM monitors the engine through a number of
different sensors to ensure optimal 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-04 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
Figure 2. G643 LP System
The LPG regulator and the mixer operate as an
open loop system since no mixture adjustments are
made by the SECM. The mixer does have an idle
mixture adjustment and a power valve adjustment.
Manifold pressure from the TMAP, rpm from the
crank position sensor and throttle position is used by
the SECM to calculate load. Feedback from the
electronic throttle is provided to the SECM by the
throttle position sensors (TPS).
