Electronic Control Unit

The ECU, which is located under front passenger seat (Civic CRX Si) and under driver's seat (Accord SEi), contains memories for basic injector discharge durations at various engine speeds and manifold pressures. Basic injector discharge duration, after being read out from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration. Some other functions include starting control, fuel pump control, fuel cut-off control and a fail-safe system monitor.

At start-up, air/fuel ratio must be enriched. The ECU memories contain basic discharge durations to be read out by signals from the starter switch, engine speed and coolant temperature sensors. This provides extra fuel needed for start-up.

When engine speed falls below 100 RPM, electric current to the fuel pump is cut off, preventing injectors from discharging fuel. During deceleration with the throttle valve nearly closed, electric current to the injectors is cut off at speeds over 1200 RPM, contributing to improved fuel economy. Fuel cut off action also takes place when engine speed exceeds 6600 RPM regardless of the position of the throttle valve.

A fail-safe system monitors sensors and detects any abnormalities in the ECU, ensuring safe driving even if 1 or more sensors are faulty, or if the ECU malfunctions.