JLG 740A, Service And Maintenance Manual

Page: 183 / 408

SECTION 3 - CHASSIS & TURNTABLE
3121160 – JLG Lift – 3-131
Electronic Throttle Control (ETC)
Engine speed and load control is maintained by an ETC
device. Speed and load control are determined by the
ECM. Defaults programmed into the ECM software and
throttle position sensors allow the ECM to maintain safe
operating control over the engine. The Electronic Throttle
Control device or "throttle body assembly" is connected to
the intake manifold of the engine. The electronic throttle
control device utilizes an electric motor connected to the
throttle shaft. When the engine is running electrical signals
are sent from the equipment controls to the engine ECM
when the operator depresses an equipment function
switch. The ECM then sends an electrical signal to the
motor on the electronic throttle control to increase or
decrease the angle of the throttle blade thus increasing or
decreasing the air/fuel flow to the engine.
The electronic throttle control device also incorporates
two internal Throttle Position Sensors (TPS) which provide
output signals to the ECM as to the location of the throttle
shaft and blade. The TPS information is used by the ECM
to correct speed and load control as well as emission con-
trol.
Engine Control Module
To obtain maximum effect from the catalyst and accurate
control of the air fuel ratio the emission certified engine is
equipped with an onboard computer or Engine Control
Unit (ECM). The ECM is a 32 bit controller which receives
input data from sensors fitted to the engine and fuel sys-
tem and then outputs various signals to control engine
operation.
One specific function of the controller is to maintain
"closed loop fuel control". Closed loop fuel control is
accomplished when the exhaust gas oxygen sensor
(HEGO) mounted in the exhaust system sends a voltage
signal to the controller. The controller then calculates any
correction that may need to be made to the air fuel ratio.
The controller then outputs signals to the EPR to correct
the amount of fuel being supplied to the mixer. At the
same time the ECM may correct the throttle blade position
to correct speed and load of the engine.
The controller also performs diagnostic functions on the
fuel system and notifies the operator of malfunctions by
turning on a Malfunction Indicator Light (MIL) mounted in
the Ground Control Station and the Platform Control Sta-
tion. Malfunctions in the system are identified by a Diag-
nostic Code number. In addition to notifying the operator
of the malfunction in the system the controller also stores
the information about the malfunction in its memory.
Figure 3-75. ETC throttle control device
Figure 3-76. LPG Engine Control Unit (ECM)
Figure 3-77. ECM Assembly