3114, 3116 and 3126 MUI Engine Governors Caterpillar

The fuel shutoff solenoid is used to move the fuel rack to the OFF position. When the fuel rack reaches the OFF position, the engine will shut off. There are three different types of solenoids that are used in various applications.

Latching Solenoids

Mechanical Latching Solenoid

1. This solenoid uses an internal mechanical latching system to hold the solenoid in the Run position during engine operation. There are two coils in the solenoid. The first coil is the start coil. The start coil is energized during engine cranking. The start coil pulls the plunger into the solenoid to the Fuel ON position. The plunger position is maintained mechanically by the mechanical latching system. The second coil is the stop coil. The stop coil disengages the mechanical latching system. This allows the plunger to return to the Fuel OFF position. The solenoid contains a switch that disconnects the stop coil when the solenoid is in the Fuel OFF position. During engine operation, neither one of the coils are energized.

Magnetic Latching Solenoid

1. This solenoid uses an internal magnetic latching system to hold the solenoid in the Run position during engine operation. There are two coils in the solenoid. The first coil is the start coil. The start coil is energized during engine cranking. The start coil pulls the plunger into the solenoid to the Fuel ON position. The plunger position is maintained magnetically by a permanent magnet. The second coil is the stop coil. The permanent magnet maintains the plunger position until the stop coil is activated. When the stop coil is activated, the stop coil pushes the plunger away from the magnet and the plunger spring pushes the plunger toward the Fuel OFF position. The solenoid contains a switch that disconnects the stop coil when the solenoid is in the Fuel OFF position. During engine operation, neither one of the coils are energized.

Manual Override Procedure for Latching Type Solenoids

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Illustration 1	g00523890
Fuel Shutoff Solenoid (Latching Type) (1) Knob (2) Rod (3) Plastic cap

1. Remove plastic cap (3) .

2. Pull out on rod (2) with pliers in order to place the solenoid in the RUN position. The plunger will latch in this position.

3. Pull out on knob (1) in order to unlatch the solenoid. The plunger will return to the Fuel OFF position.

Nonlatching Solenoid

1. Unlike the latching solenoids, this solenoid requires voltage during engine operation. The solenoid contains only one coil. When the coil is energized, the plunger is pulled in the Fuel ON position. When the voltage is removed from the solenoid, the plunger spring pushes the plunger to the Fuel OFF position. The engine will shut off. This type of solenoid is typically used on governors for truck applications.