JLG 450A_AJ Series II Service Manual - Manual (Page 176)

SECTION 3 - CHASSIS & TURNTABLE
3-126 – JLG Lift – 3121180
Gasoline Fuel Pump
The Gasoline is stored as a liquid in the fuel tank and in
drawn into the fuel system by an electric fuel pump. The
fuel pump receives a signal from the ECM to prime the
fuel system for approximately 2 seconds prior to start.
Priming the fuel system provides for a quicker start when
the engine begins to crank.
Gasoline Pressure And Temperature Sensor
Manifold
This engine is equipped with a fuel injector rail that does
not have a pressure regulator or a return circuit to the fuel
tank. Fuel pressure is regulated by the engine’s ECM. The
ECM receives fuel pressure and temperature feedback
from the gasoline fuel sensor manifold and uses this infor-
mation to control the ground side of the fuel pump. Fuel
pressure is regulated by the ECM pulse width modulating
(PWM) the fuel pump. The fuel pressure and temperature
sensor manifold has a return or “bleed” circuit that con-
nects back to the fuel tank. This circuit bleeds off any
vapor that develops in the line and returns a small amount
of fuel to the tank. Fuel comes from the fuel tank and
passes through the fuel pump. Fuel exits the fuel pump,
passes through the filter and then enters the fuel pressure
and temperature manifold assembly. Fuel flows through
the feed circuit and is delivered to the fuel injector rail.
Fuel that enters bleed circuits through manifold bypass
valve returns to the fuel tank.
Fuel Filter
After fuel is drawn into the fuel pump, the fuel flows
through the gasoline fuel filter. The fuel filter traps small
particles as the fuel passes through the filter to remove
debris and prevents the fuel pressure and temperature
manifold and fuel injectors from becoming damaged.
Maintenance of the fuel filter is required as indicated in
Section 1.
Fuel Injector Rail
Fuel flows from the fuel pressure and temperature mani-
fold assembly to the fuel rails where the fuel is delivered to
the fuel injectors. The fuel rail also contains a Schrader
valve which is utilized to test the regulated pressure of the
fuel system.
Fuel Injector
The fuel supply is maintained on the top of the injector
from the injector rail. The injector is fed a “pulse” signal
through the wire harness which causes the injector to
open. During regular operating conditions the ECM con-
trols the opening and duration of opening of the injector.
During lower RPM operation the injector signals or
“pulses” are less frequent then when the engine is operat-
ing at higher RPM’s. The engine has been calibrated to
deliver the precise amount of fuel for optimum perfor-
mance and emission control.
3.19 GM ENGINE FUEL SYSTEM REPAIR
Propane Fuel System Pressure Relief
THE PROPANE FUEL SYSTEM OPERATES AT PRESSURES UP TO
312 PSI (21.5 BAR). TO MINIMIZE RISK OF FIRE AND PERSONAL
INJURY, RELIEVE PROPANE FUEL SYSTEM PRESSURE (WHERE
APPLICABLE) BEFORE SERVICING PROPANE FUEL SYSTEM
COMPONENTS.
To relieve propane fuel system pressure:
1. Close the manual shut-off valve on the propane fuel
tank.
2. Start and run the vehicle until the engine stalls.
3. Turn the ignition switch OFF.
RESIDUAL VAPOR PRESSURE IS PRESENT IN THE FUEL SYS-
TEM. ENSURE WORK AREA IS WELL VENTILATED BEFORE DIS-
CONNECTING ANY FUEL LINE.
Figure 3-85. Gasoline Fuel Pressure and Temperature
Manifold Assembly