JLG 740AJ, Service And Maintenance Manual

Page: 208 / 582

SECTION 3 - CHASSIS & TURNTABLE
3-156 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 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 Engine Mod-
ule how much oxygen is in the exhaust gas. The Engine Mod-
ule 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 com-
bustion. 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 deliv-
ered 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 information.
Figure 3-79. Typical Fuel System
HIGH PRESSURE CIRCUIT - OPERATING PRESSURE 65 PSI.