Nissan Sentra/Pulsar/NX 1982-1996 Repair Guide

High Altitude Emission Control and Injection Timing Control System

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OPERATION



See Figures 1, 2 and 3



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Fig. Fig. 1: High altitude compensation system components

The high altitude emission control system is designed to control CO (carbon monoxide) and HC (hydrocarbons) and improve driveability in high altitude.

The altitude compensator is located on top of the injection pump with a pin connected to the control lever. The higher the altitude, the lower the atmospheric pressure. Due to this, the pressure inside the aneroid is higher than atmospheric pressure causing the aneroid to expand like a balloon. When this happens, the aneroid shaft is lower and the shaft and pin's contact surface is changed to decrease fuel. The system controls fuel in proportion to altitude.

The injection timing control solenoid (non-California) is installed on the top of the overflow connector of the injection pump and is connected to the bypass passage leading to the inlet connector. The solenoid valve controls the bypass passage in response to the electric signal from the EGR control unit which has a barometer built in. The valve is located below the altitude compensator.

  1. At high altitude (above 26.57 in. Hg/90.00 kPa), the solenoid valve is ON, orifice is closed, fuel circulating in the injection pump increases, fuel pressure increases and injection timing is advanced 1.5°.
  2.  
  3. At low altitude (below 26.57 in. Hg/90.00 kPa), the solenoid valve is OFF, orifice is open, fuel circulating in the injection pump decreases, fuel pressure decreases and injection timing is not advanced.
  4.  



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Fig. Fig. 2: Cross-sectional view of the altitude compensator



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Fig. Fig. 3: Cross-sectional view of the control solenoid valve

 
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