Control Of Detonation - Fiat 1998 Marea Service Manual

Marea-
Marea Weekend
99 update

Control of detonation

This strategy has the task of detecting the presence of detonation by processing the signal coming from
the appropriate sensor. The strategy continuously compares the signal coming from the sensor with a level
which is, in turn, constantly updated to take into account background noise and the ageing of the engine.
If the system recognizes the presence of detonation, the strategy reduces the ignition advance, in steps of
2° up to a maximum of 7°, until the phenomenon disappears. Later, the advance is gradually restored to
the basic value or until the onset of the phenomenon again. The advance increases are implemented
gradually, whilst the reductions are implemented immediately.
In acceleration conditions, the strategy uses a higher threshold to take into account the increased noise of
the engine under these circumstances.
The strategy is also equipped with a self-adjustment function which temporarily memorizes the reductions
in the advance which are continuously repeated in order to adapt the advance to the different conditions
in which the engine finds itselllf (for example, the use of a low octane rating fuel). The strategy is capable
of restoring the advance to the map vaule if the conditions which caused the reduction no longer exist.
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