Adaptive Functions

FUEL TRIM CONTROL - ADAPTIVE FUNCTIONS





The tolerances of certain components such as the mass air flow (MAF) sensor, the injectors and air leaks in the intake manifold will affect the fuel/air mixture. The engine control module (ECM) has adaptive functions to compensate for these factors. When the engine is new the integrator varies cyclically around a nominal median (A) 1.00 with, for example, a ±5% change in injection period when fuel trim is operating.

If there is an air leak the integrator is quickly displaced to a new position (B), operating between 1.10 (+10%) and 1.20 (+20%) for example (still with an amplitude of 5%, but displaced in relation to the original median (A)). The injection period has increased to compensate for the increased volume of air.

This increase is corrected for by the adaptive functions so that the integrator operates around its new median (B) with its full control range ±25% available.





Adaptation is a measure of the difference (C) between the original integrator median (A) and the new median (B).

The adaptive functions consist of two elements:

^ The first element (an additive term) can increase or decrease the injection period by 0.5 ms. This adaptation operates when the engine is idling. It corrects the integrator to its median within a few minutes. This is the method used by the engine control module (ECM) to adjust the CO content when the engine is idling.

^ The second element (a multiplier) can increase or decrease injection period by 25%. This adaptation operates when the engine is running at partial load.

Adaptive adjustments to injection period are continuously stored in the engine control module (ECM). This means that the engine gets the right fuel/air mixture immediately it is started and when fuel is shut-off during engine braking, even before the heated oxygen sensor (HO2S) has heated up enough to operate.