JLG 740A, Service And Maintenance Manual

Page: 158 / 408

SECTION 3 - CHASSIS & TURNTABLE
3-106 – JLG Lift – 3121160
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 manifold near each intake valve.
The main control sensor is the heated oxygen sensor
(H02S) located in the exhaust system. The H02S tells the
Engine Module how much oxygen is in the exhaust gas.
The Engine Module 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 Engine Module 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 controlled by the Engine Module. Refer to
"Open Loop and Closed Loop Operation" for more infor-
mation.
Figure 3-56. Typical Fuel System
HIGH PRESSURE CIRCUIT - OPERATING PRESSURE 65 PSI.