Feedback System

The amount of fuel injected from the fuel injector is determined by the ECM. The ECM controls the length of time the valve remains open (injection pulse duration). The amount of fuel injected is a program value in the ECM memory. The program value is preset by engine operating conditions. These conditions are determined by input signals from both the crankshaft position sensor and the mass air flow sensor.

In addition, the amount of fuel injected is compensated to improve engine performance. ECM increases injection pulse width under the following conditions:

• During warm-up.
• When starting the engine.
• During acceleration.
• Hot-engine operation.
• When selector lever is changed from "N" to "D" (A/T models).
• High-load, high-speed operation.

ECM decreases injection pulse width under the following conditions:

• During deceleration.
• During high-speed engine operation.

Fuel injection system incorporates mixture ratio feedback. The mixture ratio feedback system provides the best air-fuel mixture ratio for driveability and emission control. The three way catalyst (manifold) can then better reduce CO, HC and NOx emissions. This system uses heated oxygen sensor 1 in the exhaust manifold to monitor if the engine operation is rich or lean. The ECM adjusts the injection pulse width according to the sensor voltage signal. This maintains the mixture ratio within the range of stoichiometric (ideal air-fuel mixture). This stage is referred to as the closed loop control condition. Heated oxygen sensor 2 is located downstream of the three way catalyst (manifold). Even if the switching characteristics of heated oxygen sensor 1 shift, the air-fuel ratio is controlled to stoichiometric by the signal from heated oxygen sensor 2.

The open loop system condition refers to when the ECM detects any of the listed conditions. Feedback control stops in order to maintain stabilized fuel combustion.

• Deceleration and acceleration.
• High-load, high-speed operation.
• Malfunction of heated oxygen sensor 1 or its circuit.
• Insufficient activation of heated oxygen sensor 1 at low engine coolant temperature.
• High engine coolant temperature.
• During warm-up.
• After shifting from "N" to "D" (A/T models).
• When starting the engine.