Barometric Pressure Sensor: Description and Operation

The amount of fuel sent to the injectors is affected, in part, by the signals to the ECU from the altitude compensator.
With the ignition on or with the engine running, the altitude compensator will receive a constant voltage signal from the ECU (approx. 8 volts). As altitude increases (decreasing air pressure) the air/fuel mixture will be adjusted by a reduction of the EHA current.