High Altitude Compensation

High altitude compensation is used for compensation of air/fuel mixture (and idle speed). Fuel compensation is accomplished by mixture control solenoid supplying additional air to control air passages. High altitude compensation requirements are determined by control unit based upon signals from the high altitude compensation switch. Control unit supplies and monitors a voltage signal to the switch. At elevations less than 4000 ft., switch is open and monitored voltage is high. At elevations greater than 4000 ft., switch is closed and monitored voltage is pulled low.