Oshkosh JLG 400S, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3-78 – JLG Lift – 3120895
OPEN LOOP AND CLOSED LOOP OPERATION
The ECM 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 ECM 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
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 ECM con-
tinuously 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 ECM 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
ECM responds by reducing the “on” time of the fuel injec-
tors, 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 (ECM) to calculate the
ignition sequence. The sensor initiates the reference
pulses which the ECM uses to calculate RPM and crank-
shaft position.
ELECTRONIC IGNITION
The electronic ignition system controls fuel combustion by
providing a spark to ignite the compressed air/fuel
w
mix-
ture at the correct time. To provide optimum engine perfor-
mance, fuel economy, and control of exhaust emissions,
the ECM controls the spark advance of the ignition system.
Electronic ignition has the following advantages over a
mechanical distributor system:
• No moving parts
• Less maintenance
• Remote mounting capability
• No mechanical load on the engine
• More coil cooldown time between firing events
• Elimination of mechanical timing adjustments
• Increased available ignition coil saturation time