SECTION 3 - CHASSIS & TURNTABLE
3-104
– JLG Lift –
3120740
Fuel System
FUEL INJECTOR
The Electronic Fuel Injection (EFI) fuel injector is a solenoid-
operated device controlled by the ECM. The ECM energizes the
solenoid, which opens a valve to allow fuel delivery.
The fuel is injected under pressure in a conical spray pattern at
the opening of the intake valve. Excess fuel not used by the
injectors passes through the fuel pressure regulator before
being returned to the fuel tank.
A fuel injector which is stuck partly open will cause a loss of
fuel pressure after the engine is shut down, causing long crank
times.
FUEL METERING SYSTEM COMPONENTS
The fuel metering system is made up of the following parts:
• The fuel injectors
• The fuel rail
• The fuel pressure regulator/filter assembly
• The electronic governor
• The ECM
• The crankshaft position (CKP) sensor
• The camshaft position (CMP) sensor
• The fuel pump
• The fuel pump relay
BASIC SYSTEM OPERATION
The fuel metering system starts with the fuel in the fuel tank.
The fuel is drawn up to the fuel pump through a pre-filter. The
electric fuel pump then delivers the fuel to the fuel rail
through an inane fuel filter. The pump is designed to provide
fuel at a pressure above the pressure needed by the injectors.
A fuel pressure regulator in the fuel filter assembly keeps fuel
available to the fuel injectors at a constant pressure. A return
line delivers unused fuel back to the tank.
FUEL METERING SYSTEM PURPOSE
The basic function of the air/fuel metering system is to control
the air/fuel delivery to the engine. Fuel is delivered to the
engine by individual fuel injectors mounted in the intake man-
ifold near each intake valve.
The main control sensor is the heated oxygen sensor (H02S)
located in the exhaust system. The H02S tells the ECM how
much oxygen is in the exhaust gas. The ECM changes the air/
fuel ratio to the engine by control-ling the amount of time that
the fuel injector is "ON." The best mixture to minimize exhaust
emissions is 14.7 parts of air to 1 part of gasoline by weight,
which provides the most efficient combustion. Because of the
constant measuring and adjusting of the air/fuel ratio, the fuel
injection system is called a "closed loop" system.
The ECM monitors signals from several sensors in order to
determine the fuel needs of the engine. Fuel is delivered under
one of several conditions called "modes." All modes are con-
trolled by the ECM. Refer to "Open Loop and Closed Loop
Operation" for more information.
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