Mixture Ratio Feedback Control (Closed Loop Control)

Fig 1: Mixture Ratio Feedback Control Communication Diagram (Closed Loop Control)

Courtesy of NISSAN NORTH AMERICA, INC.

The mixture ratio feedback system provides the best air-fuel mixture ratio for driveability and emission control. The three way catalyst (manifold) can better reduce CO, HC and NOx emissions. This system uses A/F sensor 1 in the exhaust manifold to monitor whether the engine operation is rich or lean. The ECM adjusts the injection pulse width according to the sensor voltage signal. For more information about A/F sensor 1, refer to "AIR FUEL RATIO (A/F) SENSOR 1 ". 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 A/F sensor 1 shift, the air-fuel ratio is controlled to stoichiometric by the signal from heated oxygen sensor 2.

• Open Loop Control

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

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