Air-fuel ratio (AFR) or Lambda or stoichiometric mixture is an important measurement required for electronic vehicle engine control and management. Air-fuel ratio meters are very helpful in designing automotive engine control unit (ECU) and automatic speed control of vehicles by tuning Air-fuel ratio (AFR). An engine control unit (ECU), also known as power-train control module (PCM), or engine control module (ECM) is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running.

Proper engine tuning is vital to achieving maximum performance and avoiding costly component failures. Digital air/fuel meters have only offered single sensor measuring capability. Keeping the air-fuel mixture near the stoichometric ratio of 14.7:1 (for gasoline engines) allows the catalytic converter to operate at maximum efficiency. Air-fuel ratio metering helps to increase Fuel economy. An air-fuel mixture leaner than the stoichiometric ratio will result in near optimum fuel mileage, costing less per mile traveled and producing the least amount of CO2 emissions.

Lean mixtures improve the fuel economy but also cause sharp rises in the amount of nitrogen oxides (NOX). If the mixture becomes too lean, the engine may fail to ignite, causing misfire and a large increase in unburned hydrocarbon (HC) emissions. Lean mixtures burn hotter and may cause rough idle, hard starting and stalling, and can even damage the catalytic converter, or burn valves in the engine. The risk of spark knock/engine knocking (detonation) is also increased when the engine is under load.

Cold engines also typically require more fuel and a richer mixture when first started (see: cold start injector), because fuel does not vaporize as well when cold and therefore requires more fuel to properly “saturate” the air. Rich mixtures also burn slower and decrease the risk of spark knock/engine knocking (detonation) when the engine is under load. However, rich mixtures sharply increase carbon monoxide (CO) emissions.

Proper tuning of air-fuel ratio is very important in improving automobile fuel economy (or mileage) and vehicle engine long-term performance and life.