Subaru 2002 Impreza Service Manual page 116

A/F CONTROL SYSTEM
Emission Control
(Aux.
Emission Control Devices)
5. N F Control System
0
The aidfuel (A/F) control system makes a correction to the basic fuel injection duration in accor-
dance with the signal from the front oxygen sensor so that the stoichiometric ratio is maintained,
thus ensuring most effective exhaust gas purification by the three-way catalyst. Different basic fuel
injection durations are preset for various engine speeds and loads, as well as the amount of intake
air.
This system also has a "learning" control function which stores the corrected data in relation to
the basic fuel injection in the memory map. This allows an appropriate air-fuel ratio correction to
be added automatically in quick response to any situation that requires such an effect. Thus, the
air-fuel ratio is optimally maintained under various conditions while purifying exhaust gases most
effectively, improving driving performance and compensating for changes in sensors' perfor-
mance over time.
EC-8