Starting Mode (Port and TBI Injection)

When the ignition is switched On, the ECM energizes the fuel pump for two seconds and pressure is built up in the fuel rail. The ECM then checks the coolant temperature sensor, the TPS and crank signal and determines the proper air/fuel ratio for starting.
The ECM controls the air/fuel ratio by changing how long the injectors are turned on and off. This is accomplished by ``Pulsing'' the injectors for short periods of time.
The cold start valve, used on V6-173 and V8-305, 350 engines, is not controlled by the ECM. This valve is used to provide additional fuel during the starting mode of operation to improve cold start-ups. The cold start circuit is important when engine coolant temperature is very low because the other eight injectors will not be pulsed ON long enough to provide the needed amount of fuel to start the engine.