JLG 3394RT Service Maintenance Manual page 101

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 will receive a signal from the ECM to prime the
fuel system for approximately 2 seconds prior to start.
Priming of 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 for this engine is regulated by the
engine's ECM. The ECM receive fuel pressure and tem-
perature feedback from the gasoline fuel sensor manifold
and uses this information 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 connects back to the fuel tank. This circuit is
used to bleed off any vapor that develops in the line and
return a small amount of fuel to the tank. The 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 assem-
bly. Fuel flows through the feed circuit and is delivered to
the fuel injector rail. Fuel that enters the bleed circuits
through they bypass valve in the manifold is returned to
the fuel tank.
Figure 3-36. Gasoline Fuel Pressure and Temperature
Manifold Assembly
3121133
SECTION 3 - CHASSIS & SCISSOR ARMS
Fuel Filter
After the fuel is drawn into the fuel pump, the fuel flows
through the gasoline fuel filter. The fuel filter will trap 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 RPMs. The engine has been calibrated to
deliver the precise amount of fuel for optimum perfor-
mance and emission control.
– JLG Sizzor – 3-65