HOMEBeginners guide to tuning4. FUEL MANAGEMENT

Beginners guide to tuning

Fuel Management

In order to burn fuel completely, it is necessary to have approximately 15g of air for every 1g of fuel (15:1) and this is called stoichiometric air fuel ratio. However, in practice an engines air fuel ratio tends to be richer in fuel than the stiochiometric ratio due to conditions like the atomisation of fuel (how well the fuel mixes with air) and the cooling effect that the fuel has on the engine. An A/F (air fuel) gauge is used to measure the ratio and many stock control systems will use an O2 sensor to make rough adjustments. Under normal conditions, the cars on board computer measures the amount of air that the engine has drawn in using an air flow meter, and calculates the necessary amount of fuel needed. This relies on the vehicle being under standard conditions and once the amount of air is altered through "boost up" or similar, then fuelling should generally be adjusted to suit. When setting the fuelling, it is possible to draw on experience but the use of an A/F gauge and a data logger, which can record various different parameters, is common practice.
 HKS has developed F-CON as a product which can control fuelling. Alterations are made to the injector signal to control the volume of fuel under various circumstances. It is also possible to alter the air flow meter signal to make the stock computer detect a different air flow to what is actually present to affect the fuelling. HKS AFR and FCD are products of this type.

F-CON V Pro is compatible with D-Jetronic systems

L-Jetronic system vs D-Jetronic system

In many conventional setups, the amount of fuel to be injected is calculated though an air flow meter using what is often referred to as an L-Jetronic system. L-Jetronic systems typically use a hotwire or sprung sensor which is placed in the intake piping which can restrict air flow and also has limitations to the volume of air they can measure. D-Jetronic systems use a pressure sensor inside the intake manifold to measure the amount of air present and so it becomes more efficient for air flow. D-Jetronic systems can also be known as "airflow-less" and using F-CON V Pro can turn an L-Jetronic system into a D-Jetronic one.