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Basic fuel quantity

Basic fuel quantity


The mass air flow sensor grounds the control module's input with a frequency which is dependent on the mass air flow. When the mass air flow increases, the frequency will also increase. The control module converts the frequency to grams air/second (g/s).

Most interesting, however, is the air mass that is drawn in by each cylinder, as it is to this air the petrol is to be added. The control module registers the air mass drawn in during one engine revolution. As the engine is 4-cylinder 4-stroke, two cylinders must have drawn in air simultaneously during this engine revolution. The air mass passing the mass air flow sensor is divided by two so that the control module will be aware how much each cylinder has drawn in. The unit has now changed to milligrams air/combustion (mg/c).

To achieve lambda = 1, there must be a specific fuel/air ratio, namely 1 kg fuel to 14.7 kg air. As we know how much air has been drawn into each cylinder per combustion, the co ntrol module can easily calculate how much fuel is to be injected into the cylinders each time. The milligrams air/combustion figure is divided by 14.7 and the result is the number of mg fuel/combustion to be injected into each cylinder.

The Compensation section, see , explains why the basic fuel quantity must sometimes be adjusted to a leaner, or more frequently, a slightly richer mixture for the engine to function well and for emissions to be kept within the prescribed limits.