TM 5-3805-280-24-2
Fuel System Operation and Tests
COLD START ADVANCE SYSTEM OPERATION (ROTARY PUMPS)
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LUCAS COLD START ADVANCE
To comply with exhaust emissions regulations, the
timing of injection pumps should be around 6--9
On engines equipped with Lucas injection pumps, the
degrees before TDC. This timing value does not allow
major components of the cold start advance system
for proper start-up when the engine is cold. A cold
are the cold start advance switch, wax motor, cold
start advance system is used to temporarily advance
start advance piston and springs, auto advance
injection pump timing during cold engine start-up
housing, piston and springs.
conditions.
The cold start advance switch is mounted in the water
STANADYNE COLD START ADVANCE
manifold/thermostat housing. The switch is normally
open at coolant temperatures below 60 C (140F). At
On engines equipped with Stanadyne injection pumps,
cold start-up, there is no current flow to the wax motor.
the major components of the cold start advance
Maximum fuel pressure is applied to the auto advance
system are the cold start advance switch, cold start
piston and engine timing is advanced 7--10 degrees.
advance solenoid and cold start advance piston.
When engine coolant temperature raises above 60 C
The cold start advance switch is mounted in the water
(140F), the cold start advance switch closes and
manifold/thermostat housing. The switch is normally
closed at coolant temperatures below 60 C (140F),
current flows to the wax motor. A heating element in
the wax motor heats the wax, causing it to expand. As
providing current to energize the cold start solenoid. At
the wax expands, the wax motor plunger extends,
cold start-up, the solenoid plunger is unseated,
opening a ball valve and applying fuel pressure to the
allowing pressurized fuel to flow to the cold start
cold start advance piston. Equal pressure between the
advance piston. Piston movement advances engine
cold start advance piston and the auto advance piston
timing 7--10 degrees.
and the net force applied to the advance springs
When engine coolant temperature raises above 60 C
returns injection pump timing to normal operating
(140F), the cold start advance switch opens, cutting
levels.
off current flow to the solenoid. The solenoid plunger
seats, cutting off fuel flow to the cold start advance
piston and timing returns to normal operating levels.
DPSG,OUO1004,122 1913MAY981/1
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