The thermo-time switch controls the cold start valve so that the engine will not flood if it does not start immediately.
Some cars also have a hot start pulse relay installed; this relay operates the cold start valve intermittently during cranking, even when the engine coolant is warm. This additional fuel aids hot starting.
The cold start valve is an electrically operated solenoid valve.
When voltage is applied, additional fuel is sprayed directly into the intake manifold.
When the valve is not energized it closes and seals.
The thermo-time switch senses cold engine temperature and controls the cold start valve opening time.
Cold Start Valve Wiring
The cold start valve is wired so that it opens:
- Continuously, for several seconds when the starter is activated and the thermo-time switch provides a ground (cold engine). or
- Intermittently, when the starter is activated and the Hot Start Pulse Relay provides a ground (warm engine).
When making a compression test on cars with a Hot Start Relay, the cold start valve should be disconnected. This will prevent the cold start valve from spraying fuel while cranking.