# JD 5303 cold starting circuit



## Fedup (Feb 25, 2014)

Just a side note - don't bother replacing the culprit temp sensor. The circuit it's involved with is often referred to as a "cold start solenoid". The purpose for it is to alter pump timing by a few degrees on cold startup. Merely an emissions trick, and in reality, has no effect on cold starting at all. You'll get by just fine without it and never notice the difference.


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## drmonsterbrain (Jun 7, 2013)

In response to Fedup: The terminology depends on the pump being referred to. Depending on the ambient temps there may or may not be a difference in startup. Someone from the south can forget about it in winter and probably never notice. However if you're from my home state of Michigan, it would definitely be noticed. I have provided some additional information for all to read and each may make their decisions accordingly.

To comply with exhaust emissions regulations, the timing of injection pumps should be around 6—9 degrees before TDC. This timing value does not allow for proper start-up when the engine is cold. A cold start advance system is used to temporarily advance injection pump timing during cold engine start-up conditions.

*Stanadyne Cold Start Advance*
On engines equipped with Stanadyne injection pumps, the major components of the cold start advance system are the cold start advance switch, cold start advance solenoid and cold start advance piston.

The cold start advance switch is mounted in the water manifold/thermostat housing. The switch is normally closed at coolant temperatures below 60°C (140°F), providing current to energize the cold start solenoid. At cold start-up, the solenoid plunger is unseated, allowing pressurized fuel to flow to the cold start advance piston (D). This forces advance piston (E) to the fully advanced position, advancing engine timing 7—10 degrees.

When engine coolant temperature rises above 60°C (140°F), the cold start advance switch opens, cutting off current flow to the solenoid. The solenoid plunger seats, cutting off fuel flow to the cold start advance piston (D) and timing returns to normal operating levels.

*Delphi/Lucas Cold Start Advance*
On engines equipped with Delphi/Lucas injection pumps, the major components of the cold start advance system are the cold start advance switch, motor or solenoid, cold start advance piston and springs, auto advance housing, piston and springs.

The cold start advance switch is mounted in the water manifold/thermostat housing. The switch is normally open at coolant temperatures below 60°C (140°F). At cold start-up, there is no current flow to the motor or solenoid. Maximum fuel pressure is applied to the auto advance piston and engine timing is advanced 5—10 degrees.

When engine coolant temperature rises above 60°C (140°F), the cold start advance switch closes and current flows to the actuating mechanism (motor / solenoid). The actuator extends, opening a ball valve and applying fuel pressure to the cold start advance piston. Equal pressure between the cold start advance piston and the auto advance piston and the net force applied to the advance springs returns injection pump timing to normal operating levels.


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