Beginning in 1989, pumps have altitude and load compensating features. The altitude compensation feature automatically leans the mixture at higher altitudes to compensate for less dense air. This reduces smoke in the exhaust. A barometric element is connected by vacuum hose to a compensating valve on the injection pump. As the element expands at higher altitudes, it acts on the valve and reduces the injection quantity of the pump. The load compensating feature increases injection quantities under certain load conditions. It is controlled by a pressure switch which activates a solenoid on the pump. Below 900 m (3000 ft.) the pressure switch should be open. Above 1250 m (4100 ft.) the switch should be closed. The barometric element is mounted on the side of the engine compartment. The pressure switch is mounted on the barometric element.