Pressure Sensor
This sensor is mounted on firewall. An electrically controlled solenoid valve is connected to sensor. The solenoid valve has 2 hoses connected to it. One hose connects to air cleaner duct and other hose connects below throttle valve.
The solenoid valve is activated by ECU whenever ignition switch is turned to "ON" or "START" positions, for a specific period of time. When activated, the solenoid measures ambient barometric pressure from above throttle valve. Ambient barometric pressure changes due to weather and/or altitude. This information is sent to ECU for controlling fuel delivery time.
After a predetermined period of time, solenoid valve is deactivated by ECU. When deactivated, the solenoid measures intake manifold pressure below throttle valve. The ECU compares barometric pressure and intake manifold pressure and an absolute value is used to determine fuel delivery and ignition timing.
The pressure sensor and solenoid valve are also used for altitude compensation. These components inform ECU of altitude. The ECU calculates air/fuel ratio necessary for engine operation in high altitude areas.