G643(E) Service Manual Chapter 5. Engine Management System (EMS) 171
Limp Home Mode
The system is capable of "limp-home" mode in the
event of particular faults or failures in the system. In
limp-home mode the engine speed is approximately
1000 rpm at no load. A variety of fault conditions can
initiate limp-home mode. These fault conditions and
resulting actions are determined during calibration
and are OEM customer specific.
Service Tool
A scan tool/monitoring device is available to monitor
system operation and assist in diagnosis of system
faults This device monitors all sensor inputs, control
outputs, and diagnostic functions in sufficient detail
through a single access point to the SECM to allow
a qualified service technician to maintain the system.
This Mototune software (licensed by Mototron
Communication) is secure and requires a crypt-
token USB device to allow access to information.
LPG Fuel System Operation
The principles outlined below describe the operation
of MI-07 on an LPG fuel system.
An LPG fuel system consists of the following
components:
• Fuel filter (supplied by customer)
• Electric fuel lock-off solenoid valve
• Fuel pressure regulator/vaporizer
• Gas/Air mixer
• Miscellaneous customer-supplied hoses and
fittings
Fuel is stored in the customer-supplied LPG tank in
saturated liquid phase and enters the fuel system
from the tank as a liquid and at tank pressure. Fuel
passes through a high-pressure fuel filter and lock-
off solenoid, and is then vaporized and regulated
down to the appropriate pressure to supply the
mixer. The regulator controls the fuel pressure to the
gas/air mixer. The mixer meters fuel delivery based
upon airflow into the engine.
SECM
The Small Engine Control Module (SECM) controls
the LPG lock-off solenoid valve. The lock-off
solenoid is energized when fueling with LPG and the
engine is turning. The lock-off is de-energized when
engine rpm is not detected.
MI-07 LP Fuel Filter
The LP fuel filter of G643 engine is the same as that
of G643E engine. See, “G643E EMS overview”
MI-07 Fuel Lock-Off (Electric)
The LP fuel lock-off of G643 engine is the same as
that of G643E engine. See, “G643E EMS overview”
N-2001 Regulator/Converter
After passing through the electric fuel lock-off, liquid
propane enters the N-2001 regulator/converter
(Figure 4). The N-2001 functions as a fuel vaporizer,
converting liquid propane to vapor propane and as a
two-stage negative pressure regulator, supplying the
correct vapor propane fuel pressure to the mixer.
The regulator is normally closed requiring a vacuum
signal (negative pressure) to allow fuel to flow. This
is the second of three safety locks in the MI-07
system. If the engine stops, vacuum signal stops
and fuel flow will automatically stop when both the
secondary (2nd stage) valve and the primary (1st
stage) valve closes. Unlike most other
regulator/converters, the N-2001 primary valve
closes with fuel pressure rather than against
pressure, extending primary seat life and adding
additional safety.
Figure 4. N-2001 Regulator
Liquid propane must be converted into a gaseous
form in order to be used as a fuel for the engine.
When the regulator receives the desired vacuum
signal it allows propane to flow to the mixer. As the
propane flows through the regulator the pressure is
reduced in two stages from tank pressure to slightly
less than atmospheric pressure. As the pressure of
the propane is reduced the liquid propane vaporizes
and refrigeration occurs inside the regulator due to
the large temperature drop inside the regulator from
the vaporization of liquid propane. To replace heat
lost to vaporization, engine coolant is supplied by
the engine driven water pump and pumped through
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