Pressure Sensor
The solenoid valve is temporarily activated by ECU whenever ignition switch is turned to "ON" or "START" positions. 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. See Fig 1 .
After a predetermined period of time, solenoid valve is deactivated by ECU and solenoid measures intake manifold pressure below throttle valve. The ECU compares barometric pressure to 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.