Lull 944E-42 Service Manual - Manual (Page 673)

9.163 Model 644E-42/944E-42 Rev. 6/04
Electrical System
9.11 ENGINE START CIRCUIT
The purpose of the engine start circuit is to energize the
starter solenoid and engage the starter motor to start the
engine. To start the engine, the ignition switch (1) must be
in the START (2) position, parking brake switch must be
in the ON position and transmission shift control switch
(travel select lever) must be in the NEUTRAL DETENT
(center) position.
When the ignition switch is turned to the START (2)
position, and with the transmission in NEUTRAL
DETENT (N), the starting circuit activates the starter
relay, starter solenoid, and fuel shutoff solenoid. The fuel
shutoff solenoid opens a valve that supplies fuel to the
injection pump.
9.11.1 Starting Circuit
The starting circuit functions as follows:
1. 12V direct current from the battery flows through the
positive (+) battery cable to the starter solenoid.
2. 12V direct current also flows through the ignition
switch circuit breaker and to the ignition switch.
3. When the ignition is turned to the START (2)
position, current flows through contacts in the
ignition switch, through the fuse panel, to the parking
brake switch.
4. If the parking brake is set, current flows through
contacts in the brake switch to the neutral start relay.
5. If the transmission select lever is in NEUTRAL
DETENT (N), current flows through the neutral start
relay to energize the coil of the engine start relay.
(This closes the contacts in the engine start relay.)
The engine start relay contacts close and current
flows to the engine start solenoid. (The flow of
current closes internal contacts in the engine start
solenoid that allow current to flow through starter
solenoid.) The engine start solenoid coil energizes
and its contacts close allowing current to flow to the
starter motor.
6. The starter solenoid engages a gear on the starter
pinion shaft to mesh with the flywheel, and the
starter pinion and gear begin to spin, in turn rotating
the flywheel, crankshaft and related components
within the engine.
7. When the ignition switch was initially turned, the fuel
shutoff solenoid opened a valve to supply to the fuel
injection pump. As the starter rotated the engine
components, the fuel injection pump and related
lines and injectors supplied fuel to the cylinders.
8. When the pistons compress injected fuel, ignition
occurs, the engine starts and the starter pinion
retracts.
9. As the engine runs it operates an alternator that
recharges the battery used during the starting cycle.
10. When the ignition switch is released after starting the
engine, the ignition switch returns to the neutral
RUN (3) position where it directs current to the fuse
panel that distributes electrical current for the
operation of vehicle controls, including the joystick,
gauges and other equipment.
MU1250
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