JLG 740AJ, Руководство по обслуживанию и ремонту

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SECTION 3 - CHASSIS & TURNTABLE
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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-pro-
grammed 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 tempera-
ture).
• 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 operat-
ing in "closed loop." In closed loop, The Engine Module contin-
uously adjusts the 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
Engine Module responds by increasing 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 cam-
shaft position. The CMP signal is created as piston #1 is a pre-
determined number of degrees after top dead center 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 calculate RPM and crank-
shaft position.