Fiat Bravo Service Manual page 356

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Fuel vapour recovery
The (pollutant in terms of the regulations) fuel vapours are sent to an active charcoal filter and from
there towards the engine where they are burnt; this takes places by means of a solenoid valve which is
operated by the control unit only when the engine is in a load condition which allows the correct com-
bustion without the operation of the engine being "disturbed": in effect, the control unit compensates
for this quantity of petrol entering with a reduction of the supply to the injectors.
Checking detonation
The function has the task of detecting the presence of the phenomenon of detonation (engine knock-
ing) by processing the signal coming from the relevant sensors. The control unit constantly compares
the signals coming from the sensors with a threshold value which, in turn, is continuously updated, to
take into account background noise and the ageing of the engine.
The control unit is therefore capable of detecting detonation (or the early stages of detonation) and
makes provisions to reduce the ignition advance (from 3° up to maximum of 9.7°), until the phe-
nomenon disappears. Afterwards the advance is gradually restored until the basic value is reached.
In acceleration conditions, a higher threshold is used, to take into account the greater noise produced by
the engine in these circumstances. The detonation control strategy is also equipped with a self-adjust-
ment function which ensures the memorizing of the advance reductions which should be constantly re-
peated to adapt to the different conditions in which the engine finds itself.
Checking phase transformer
The control unit controls the solenoid valve which controls the phase transformer depending on the en-
gine load conditions. When the temperature of the coolant exceeds 40 °C and when the engine speed is
higher than the idle speed and lower than 4,800 rpm with the butterfly angle greater than about 8°, the
control unit sends a signal to the solenoid valve which is activated and allows the transformer to de-
crease the timing diagram for the inlet stage by 18° (torque operation).
When the engine is idling or the speed exceeds 4,800 rpm, the control unit deactivates the solenoid
valve and the transformer restores the inlet timing to the previous basic values.
Obviously the control of the phase transformer operates with a hysteris field, i.e. the activating level for
the solenoid valve is always higher than the deactivating level; this is designed to prevent balance con-
ditions and a consequent too rapid succession passing from one timing diagram to another with obvious
operating problems.
Connection with the climate control system
When the climate control is switched on the compressor absorbs power from the engine which, when
idling, tends to cut out. To prevent this problem the control unit adjusts the air flow rate to the new
power requirements, controlled by the appropriate actuator (this adjustment also takes place during us-
age conditions to maintain optimum "driveability"). Another function of the system is that of momen-
tarily interrupting the supply to the compressor in the case of high power requirements by the engine
(strong acceleration).
System self-adjustment
The control unit is equipped with a self-adjustment function which has the task of recognizing the
changes which take place in the engine due to the settling processes which take place over a period of
time and the ageing of both the components and the engine itself.
These changes are stored in the memory in the form of modifications to the basic map and have the task
of adpating the operation of the system to the gradual alterations to the engine and the components in
relation to the characteristics when new.
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E n g i n e
Fuel system
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