TM 5-3895-382-24
Cold Start Advance Unit
The following rotary fuel injection pumps may have a cold start
advance unit: Stanadyne, Lucas and Bosch. The cold start
advance holds the timing of the fuel injection pump in an
advance position when the engine is cold.
The cold start advance unit is on the rear of the timing case on
the left side of the engine.
Stanadyne Fuel Injection Pumps
When the engine is cold, the coolant temperature switch is
closed. When the switch is closed, a 12 volt current is carried
to the solenoid. The solenoid is on the lower rear part of the
fuel injection pump. The solenoid is then actuated, resulting in
the advance of the injection timing. This produces reduced
white smoke and reduced emissions during cold weather
operation. When the coolant temperature reaches a certain
temperature, the switch opens. When the switch is open, the
switch stops the electrical current to the solenoid. The fuel
injection timing is then returned to the normal running mode.
The engine will run in the retarded mode at all times if one of
the following events occur: A wire is disconnected and the
switch fails in the open mode. The engine will then be more
difficult to start. The engine will then emit white smoke.
If the switch fails in the closed mode, the engine will run in the
advanced timing mode at all times. The result will be higher
cylinder pressure and possible engine damage.
Lucas Fuel Injection Pump and Bosch
Fuel Injection Pump
When the engine is cold, the coolant temperature switch is
open. The coolant temperature switch will then interrupt the
electrical current that goes to the wax motor. The wax motor is
in the fuel injection pump. The fuel injection pump timing is
then in the advanced position for reduced white smoke and
improved emissions. Once the coolant temperature rises, the
switch closes. The fuel injection timing is retarded.
If a wire is disconnected or if the switch fails in the open
position, the engine will run with advanced timing. The engine
will have higher cylinder pressure and engine damage may
result.
If the switch fails in the closed mode, the engine will run in the
retarded mode. The engine will then be more difficult to start.
The engine will also emit white smoke.
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