JLG 740AJ Service Manual - Manual (Page 181)

SECTION 3 - CHASSIS & TURNTABLE
3121160 – JLG Lift – 3-129
3.28 GM ENGINE DUAL FUEL SYSTEM
NOTE: +20° F (-6.6° C) is the low temperature limit for LP
gas, for both starting and operation. This applies to
all LP gas powered engines.
The Dual Fuel system allows the operator to operate the
vehicle on either gasoline or LPG by positioning a selector
switch in the operator's platform. When the operator
places the selector switch in the gasoline mode the gaso-
line fuel pump is energized. While in the gasoline mode
the LPG fuel lock-off is isolated and will not energize. In
addition the gasoline injector circuit is enabled and injec-
tor pulses are provided to each injector and the ECM cali-
bration for gasoline is also enabled. When the operator
selects the LPG mode the Low Pressure LPG lock-off is
energized and fuel from the LPG tank flows to the Elec-
tronic Pressure Regulator (EPR). The EPR receives an
electronic signal to position the secondary lever for the
start or run positions and when the engine begins to crank
the mixer air valve will rise and fuel will begin flowing to
engine. During this mode the gasoline fuel pump is iso-
lated and will not be activated. The primary components
of the gasoline dual fuel system are the gasoline tank,
electric fuel pump and filter, fuel supply line, injector rail
and injectors and the fuel pressure regulator. The primary
components of the LPG dual fuel system are the LPG fuel
tank, in-fuel filter, LPG Low Pressure lock-off, Electronic
Pressure Regulator (EPR) and the fuel mixer module. The
LPG fuel system operates at pressures which range from
14.0 inches (355.60 mm) of water column up to 312 psi
(21.5 BAR).
Components which are shared by both systems include
the Electronic Throttle Control and the ECM. The ECM
contains a dual calibration; one controls the gasoline fuel
system during gasoline operation and one controls the
LPG fuel system during LPG operation.
Fuel Filter
Propane fuel like all other motor fuels is subject to con-
tamination from outside sources. Refueling of the equip-
ment’s tank and removal of the tank from the equipment
can inadvertently introduce dirt and other foreign matter
into the fuel system. It is therefore necessary to filter the
fuel prior to entering the fuel system components down-
stream of the tank. An inline fuel filter has been installed in
the fuel system to remove the dirt and foreign matter from
the fuel. The inline filter is replaceable as a unit only. Main-
tenance of the filter is critical to proper operation of the
fuel system and should be replaced as Section 1. In
severe operating condition more frequent replacement of
the filter may be necessary.
Electric Lock Off
The Electric Lock Off device is an integrated assembly.
When energized the solenoid opens the valve and allows
the Propane fuel to flow through the device. The valve
opens during cranking and run cycles of the engine. The
lock off supply voltage is controlled by the engine control
module (ECM).
EPR Assembly
The EPR assembly is a combination Low Pressure Regu-
lator and a Voice Coil Assembly. The Voice coil is an elec-
tronic actuator which is controlled by an internal
microprocessor. The microprocessor provides output data
to the ECM and receives input data over a CAN BUS con-
nection. The internal microprocessor receives electrical
signals from the Fuel Pressure Sensor FPS and the Fuel
Temperature Pressure FTP and communicates the data to
the ECM. The ECM uses the FPS and FTP data to calcu-
late the location of the secondary lever in the LPR and
sends that data back to the EPR via the CAN BUS. The
internal microprocessor in the EPR will then output a sig-
nal, which causes the voice coil to move and position the
secondary lever to the correct location.
Figure 3-71. Electric Fuel Lock Off
1. Pressure Regulator Section
2. Fuel Inlet
3. Coolant Passage 4. Primary Test Port
5. Secondary Test Port
6. Voice Coil Section
Figure 3-72. EPR Assembly