Cranking Circuit Function
To energize the starting motor solenoid and engage the starting motor.
Cranking Circuit Operating Conditions
– PTO switch OFF
– Transmission in NEUTRAL
– Key switch in the START position
Cranking Circuit Theory of Operation
Engine operation is monitored and managed by the instrument control cluster. Moving the key switch to RUN supplies the switched power circuit and activates the cluster.
The START position of the key switch, along with the neutral, brake, seat, and PTO switches, supply input signals to the control cluster logic circuits. If all conditions are met, the cluster energizes the start relay coil. The relay connects the power at the key switch START terminal to the starting motor solenoid. As the solenoid plunger retracts, the starter pinion gear engages the flywheel, allowing the starting motor to crank the engine.
Pulses from the alternator, normally used by the tachometer to display engine speed, are also used by the control cluster logic to protect the starting motor. The cranking process can occur only if the sensed engine speed is <400 rpm (perceived by the cluster as a non-running engine). An engine speed of >800 rpm for 3 seconds, or a cranking attempt exceeding 20 seconds, ends the cranking sequence, even if the key switch is held in the START position.
Fuel Supply Function
To supply and regulate the flow of fuel to the engine.
Fuel Supply Operating Conditions
Key switch in the START or RUN position
Fuel Supply Theory of Operation
The instrument control cluster, fuel pump, and fuel shutoff solenoid work together in regulating the flow of fuel to the engine. Moving the key switch to RUN supplies the switched power circuits, activating the fuel pump and control cluster. After confirming that the conditions required to crank the engine are present, the control cluster then briefly (≈1 sec.) triggers the fuel shutoff relay. This permits the relay to apply a pulse of current to the pull-in coil of the fuel shutoff solenoid, opening the fuel passage. The solenoid hold-in coil, powered by the cluster, keeps the fuel passage open.
Glow Plug Function
To provide an added source of heat for the combustion chamber during startup.
Glow Plug Operating Conditions
Key switch in the START or RUN position
Glow Plug Circuit Theory of Operation
High levels of battery current are required to heat the glow plugs. To switch these heavy currents, the instrument control cluster employs a glow plug relay. A dedicated wire and fuse link connects the battery to the relay.
When power from the key switch first activates the control cluster, the glow plugs (via the relay) and glow plug indicator light are initially powered for five seconds. The glow plugs will also be energized as long as the engine is in crank mode.
