Electronic Control Unit (Ecu)

The ECU consists of a printed circuit board enclosed in a metal box. The ECU receives various signals from data sensors and switches. These signals are processed by the ECU for controlling fuel delivery.

The amount of fuel delivered is determined by the time that injectors are open, because the fuel pressure regulator maintains a constant pressure drop across injectors. The frequency and duration of injection (fuel delivery time) is controlled by ECU.

The ECU monitors the various engine and vehicle operations and computes the fuel delivery time. The fuel delivery time is modified for such operating conditions as engine cranking, cold starting, altitude, acceleration and deceleration.

When ignition switch is turned to "START" position, ECU calculates fuel delivery based primarily upon coolant temperature and throttle position. ECU sends an electrical signal to injectors to provide fuel for prescribed period of time. After ignition switch is released from "START" position and engine speed is above a specified RPM, ECU changes enrichment signal.

Immediately after engine starts, the ECU issues electrical signals to injectors to provide stable combustion. During engine warm-up, the ECU monitors all data sensor information and provides a richer mixture until coolant temperature reaches a preset value.

When coolant temperature exceeds preset value, ECU processes other data sensor information and issues appropriate electrical signals to injectors. This period of time is referred to as open loop mode of operation. The ECU controls fuel delivery based upon open loop programmed information until the oxygen sensor is warm enough to send modifying signals to ECU.

When the oxygen sensor is warm enough, the ECU accepts oxygen sensor information and uses it for controlling fuel delivery. When the ECU is accepting oxygen sensor information, this is referred to as closed loop mode of operation.

During closed loop operation, the ECU stores the mean values of feedback signals used to maintain optimum air fuel ratio. During open loop operation, the ECU uses these mean values to modify pre-programmed information. By doing this, the ECU can more closely control exhaust emissions even when engine is in open loop mode of operation.