Starting Mode (Port and TBI Injection)

When the ignition is first turned "ON," the Electronic Control Module (ECM) turns "ON" the fuel pump relay for two seconds and the fuel pump builds up pressure. The ECM then checks the Coolant Temperature Sensor (CTS) and Throttle Position Sensor (TPS) and determines the proper air/fuel ratio for starting.

This ranges from 1.5:1 at -36°C (-33°F) to 14.7:1 at 94°C (201°F) running temperature. The ECM controls the amount of fuel delivered in the starting mode by changing how long the injectors are turned "ON" and "OFF." This is done by "pulsing" the injectors for very short times.