Feedback System

WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2000 Nissan Xterra, 2000 Nissan Sentra, 2000 Nissan Quest, 2000 Nissan Pathfinder, and 2000 Nissan Maxima. However, it is still accessible from the selected car via links, so may be relevant.

ECM calculates base injection pulse width by processing signals from CMP sensor and mass airflow sensor. After receiving signals from sensors detecting engine conditions, ECM adds fuel enrichment (preprogrammed into control unit) to base injection pulse width to improve engine performance under the following conditions:

During warm-up.
Starting
During acceleration.
Hot engine operation.
When transmission is shifted from Neutral to Drive (A/T models).
Heavy-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. It is designed to maintain a precise mixture ratio. Through input signals from heated oxygen sensor, ECM can adjust air/fuel ratio to optimally control exhaust emissions and engine performance. This function takes place during closed loop operation. ECM continuously monitors itself to stay within an acceptable emissions output range. However, this feedback system can be overridden and will operate in open loop when one or more of the following conditions exist:

Starting.
Engine and/or oxygen sensor cold.
Driving at high speeds and under heavy load.
Malfunction of front heated oxygen sensor or circuit exists.
Vehicle is decelerating.
High engine coolant temperature.