JLG 450A_AJ Series II Service Manual - Manual (Page 155)

SECTION 3 - CHASSIS & TURNTABLE
3121180 – JLG Lift – 3-105
ELECTRONIC GOVERNOR AND THROTTLE BODY
In the 2.5L EFI industrial engine, throttle control is
achieved by using an electronic governor controlled by
the engine control module (ECM).
The electronic governor consists of a throttle body, an
electronically-actuated throttle plate, and a built-in throttle
position (TP) sensor. There are two pigtails that exit the
governor body. The 3-wire pigtail connects the TP sensor
to the ECM. Refer to “Throttle Position (TP) Sensor” for
more information.
The 2-wire pigtail carries throttle signal from ECM to gov-
ernor. Engine speeds are stored in the configuration pro-
gram for each specific application, and can be changed
with ECM calibration software. When engine speed is
selected with the toggle switch, the ECM sends the appro-
priate signal to the governor. This is a pulse-width modu-
lated (PWM) signal that cannot be read with conventional
diagnostic tools such as a voltmeter. A 12-volt signal is
pulsed on and off at a high rate of speed. The width of the
“on” pulse determines throttle opening. The ECM sends a
signal with the appropriate pulse width to the governor
based on the operator's choice of switch settings.
The electronic governor also acts as an idle air control
(IAC) valve. Changes in engine load are detected by the
ECM by comparing manifold absolute pressure (MAP)
with throttle position. When the ECM detects a change in
engine load, it can adjust idle speed by changing the
PWM signal to the governor.
OPEN LOOP AND CLOSED LOOP OPERATION
The ECM operates in the following two modes:
• Open loop
• Closed loop
When the engine is first started, the system is in “open
loop” operation. In open loop, the ECM ignores the
heated oxygen sensor (HO2S) signal. it uses a pre-pro-
grammed routine to calculate air/fuel ratio based on
inputs from the TP, ECT, and MAP sensors.
The system remains in open loop until the following condi-
tions are met:
• The HO2S has a varying voltage output showing it is
hot enough to operate properly.
• The ECT has reached 160°F (71°C).
• Seven minutes has elapsed since starting engine.
After these conditions are met, the engine is operating in
“closed loop.” In closed loop, The ECM continuously
adjusts air/fuel ratio by responding to signals from the
HO2S (except at wide-open throttle). When the HO2S
reports a lean condition (low sensor signal voltage), the
ECM enriches the mixture by increasing fuel injector “on”
time. When the HO2S reports a rich condition (high sen-
sor signal voltage) the ECM leans out the mixture by
reducing fuel injector “on” time.
CAMSHAFT POSITION (CMP) SENSOR
The CMP sensor uses a variable reactor sensor to detect
camshaft position. The CMP signal is created as piston #1
is a predetermined number of degrees after top dead cen-
ter on the power stroke.