JLG 740A, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3-108 – JLG Lift – 3121160
The electronic governor also acts as an idle air control
(IAC) valve. Changes in engine load are detected by the
Engine Module by comparing manifold absolute pressure
(MAP) with throttle position. When the Engine Module
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 Engine Module will operate 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 Engine Module ignores
the signal from the heated oxygen sensor (HO2S). it uses
a pre-programmed routine to calculate the 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 that it
is hot enough to operate properly (this depends on
temperature).
• The ECT has reached 160°F (71°C).
• Seven minutes has elapsed since starting the engine.
After these conditions are met, the engine is said to be
operating in "closed loop." In closed loop, The Engine
Module continuously adjusts the air/fuel ratio by respond-
ing to signals from the HO2S (except at wide-open throt-
tle). When the HO2S reports a lean condition (low sensor
signal voltage), the Engine Module responds by increas-
ing the "on" time of the fuel injectors, thus enriching the
mixture. When the HO2S reports a rich condition (high
sensor signal Voltages the Engine Module responds by
reducing the "on" time of the fuel injectors, thus leaning
out the mixture.
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.
CRANKSHAFT POSITION (CKP) SENSOR
The crankshaft position (CKP) sensor provides a signal
used by the engine control module (Engine Module) to
calculate the ignition sequence. The sensor initiates the
reference pulses which the Engine Module uses to calcu-
late RPM and crank-shaft position.