Emission Control Systems: Testing and Inspection

This system is designed to control the formation of hydrocarbon and carbon monoxide emissions and improve driveability at high altitudes. In order to ensure decreased exhaust emissions, the injection timing must be changed and the EGR guide tube must be replaced.
The altitude compensator is located on top of the injection pump and the altitude shaft is in contact with the pin. The pin is connected to the control lever which is in contact with the governor lever.
The higher the altitude, the lower the atmospheric pressure. Therefore, the pressure inside the aneroid is higher than the atmospheric pressure at high altitudes, causing the aneroid to expand. At this time, the aneroid shaft is lower and the aneroid shaft and pin's contact surface is changed to decrease fuel. Thus, the system controls the amount of fuel supplied in proportion to the altitude.
On 1984-85 Sentra models, an injection timing control solenoid valve is installed on top of the injection pump overflow connector. The valve controls the bypass passage in response to EGR signals.