Fiat Bravo Service Manual page 223

Bravo-Brava © i ^ Engine
Fuel system
107
Checking detonation
The strategy has the task of detecting the presence of the phenomenon of detonation, by processing the
signal coming from the appropriate sensor. The strategy constantly compares the signal coming from
the sensor with a level which, in turn, is constantly updated to take into account the background noise
and the ageing of the engine.
If the system recognizes the presence of detonation, the strategy reduces the ignition advance, produc­
ing a step of 2° up to a maximum of 6°, until the phenomenon disappears. As a result, the advance is
gradually restored until the basic value or until the phenomenon arises again. In particular, the advance
increases are gradully implemented, whilst the reductions are introduced immediately.
During acceleration conditions, the strategy uses a higher level, to take into account the increased en­
gine noise under these circumstances.
The strategy is also equipped with a self-adjustment function which permanently memorizes the ad­
vance reductions which must be continuously repeated in order to adapt the advance to the different
conditions in which the engine finds itself (for example, the use of a low octane rating fuel). The strate­
gy is capable of restoring the advance to the value in the memory if the conditions which have caused
the reduction no longer exist.
ENGINE IDLE CONTROL MANAGEMENT
The general objective of the strategy is to maintain the engine speed around the memorized value (en­
gine warm: 850 rpm): the position assumed by the actuator depends on theengine speed and conditions
and the speed of the vehicle.
Starting stage
When the key is inserted the actuator assumes a position which depends on the temperature of the en­
gine and the battery voltage (open-loop position).
Engine started with accelerator pedal released
The engine speed varies according to the temperature of the engine and is constantly maintained close
to this value modifying the position of the shutter to compensate for any oscillations in the speed.
This takes place in particular when external loads are applied (power assisted steering, heated rear
windscreen, etc).
If the electric fans and the air conditioning are switched on, both of which are managed by the control
unit, the strategy manages the advance actuator as appropriate.
Normal opeartion
In these conditions the actuator is in the open-loop position.
During deceleration
In deceleration conditions outisde of idling, the control unit operates the position of the actuator
through a special curve (dash-pot curve), or it slows down the return of the shutter towards its housing,
achieving a reduction in the engine braking effect.
CHARCOAL FILTER MANAGEMENT
The strategy controls the position of the charcoal filter solenoid valve as follows:
- during the starting stage the solenoid valve remains closed, preventing the fuel vapours from enrich­
ing the mixture; this condition persists until the engine coolant reaches 25°C;
- with the engine at operating temperature, the control unit causes the solenoid valve to operate in du­
ty-cycle to control the quantity of fuel vapours sent to the inlet, according to the engine speed and
load conditions.
In the following operating conditions:
- butterfly in closed position,
- speed below 1250 rpm,
- engien load TP < 1 ms,
the operation of the solenoid valve is disabled, keeping it in the closed position.
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