ACCELERATION
Speed variation as a function of time.

ACTUATOR DIAGNOSIS
During normal driving, many Motronic functions are operational only under specific conditions. This renders it impossible to activate all actuators (such as the EGR valve) for operational checks while on the road.

ACCERERATION ENRICHMENT
During acceleration, the L-Jetronic meters additional fuel to the engine. If the the throttle is opened abruptly, the sir-fuel mixture is momentarily leaned-off, and a short period of mixture enrichment is needed to ensure good transitional response.

ACCELERATION RESPONSE
The good acceleration response is a result of "overswing" of hte air-flow sensor plate. Transitions from one operating condition to another produce changes in the mixture ratio which are utilized to improve driveability.

ADDITIVE
Chemicals added to fuel in very small sizes to improve and maintain fuel value. Detergents and corrosion inhibitors are examples of gasoline additives.

Airhead R-bikes
Way back after World War I, BMW was prohibited from making any "machines of war," which primarily included airplanes. The brass at BMW decided that they'd like to stay in business, so they borrowed an engine design that reminded them of an airplane engine -- the Boxer -- to put into a motorcycle. That engine design stayed with them for a long, long time, and its penultimate (so far) form was the Airhead.

This is an engine that has two cylinders in the Boxer layout, and is air cooled. I won't even attempt to divine at what point in history BMW started producing Airheads, as opposed to whatever came before them. The engine is also normally aspirated, via a carbeuretor on each side.

The term Airhead can actually refer to either the engine, or the bike wrapped around the engine. Basically, Airheads were produced up until 1995 in the US, with the R100 Mystic.

ALTITUDE
A measure of distance above sea level.

AIR-MASS METER
The hot-wire and hot-film air-mass meters are "thermal" load sensors. They are installed between the air filter and the throttle valve and register the air-mass flow [kg/h] drawn in by the engine. Bothe sensors operate according to the same principle.

AIR SPARK GAP
The ingnition spark arcs directly through the air-fuel mixture between the center and ground electrodes.

AIR-TEMPERATURE SENSOR
The air-temperature sensor incorporates a NTC resistor element. So that changes in intake-air temperature can be registered immediately, the resistor portrudes from the end of a trunk shaped moulding into the area of maximum air-flow speed. The 4-pole plug-and-socket connection includes the plug for the fuel injector.

AIR-FLOW SENSOR
The air-flow sensor is found between the air filter and the throttle valve, where it monitors the volumetric flow rate [m3/h] of the air being drawn into the engine.

AIR/FUEL MIXTURE
Operation of the spark-ignition engine is contingent upon availability of a mixture with a specific air/fuel ratio. The theoretical ideal for complete combustion is a mass ratio of 14.7:1, referred to as the stoichiometric ratio. In concrete terms this translates into a mass relationship of 14.7 kg of air to burn 1 kg of fuel, while the corresponding volumetric ratio is roughly 9,500 litres of air for complete combustion of 1 litre of fuel.

AIR/FUEL RATIO
Because the A/F ratio is a crucial factor in defining an engine's emissions, the engine-management system is of immense importance in determing exhaust content.

AMBIENT-PRESSURE SENSOR
The ambient-pressure sensor shares its design with the manifold-pressure sensor, but is located inside the ECU. Barometric prsseure readings are needed by systems that rely on throttle-valve aperture instead of an air-masss meter to monitor the incoming air supply. The precise data on ambient air density registered by this sensor serve as a significant factor in numerous diagnosis functions.

ANALOG-DIGITAL CONVERTER
The signals from the throttle-valve potentiometer are continous analog siganls; as are the lambda-sensor signal; the engine-temperature signal; the intake-air signal; the battery voltage; and a voltage-reference signal generated in the ECU. These analog signals are converted to data words by the analog-digital converter and transmitted to the microprocessor via the data bus.

ARTIC CAT
Manfacturer of power sports equipment and recreational vehicles