Fiat 1998 Marea Weekend, Service Manual

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Engine
Marea-Marea Weekend®**
99 update
Fuel system
10.
MANAGEMENT OF THE ENGINE IDLE
The general aim of this strategy is to keep the engine speed around the value memorized (engine warm:
850 rpm): the position assumed by the actuator depends on the speed of the engine and the speed of the
vehicle.
Starting stage
When the key is inserted, the position assumed by the actuator depends on the temperature of the engine
and the voltage of the battery (open-loop position).
Engine started with accelerator pedal released
The engine speed varies according to the temperature of the engine and is constantly kept close to this
value by altering the position of the shutter in order to compensate for any fluctuations in the speed.
This especially takes place when external loads are switched on (power assisted steering, heated rear
windscreen, etc.).
If the air conditioning and the fans are switched on, both managed by the control unit, the strategy man-
ages the actuator in advance of the switching on.
Normal driving
In these conditions the actuator is in the open-loop position.
In deceleration conditions
In deceleration conditions outside of idling, the control unit controls the position of the actuator by means
of a special flow rate curve (dash-pot curve), in other words it slows down the return of the shutter to its
housing, reducing the braking effect of the engine.
MANAGEMENT OF THE CHARCOAL FILTER
This strategy controls the position of the charcoal filter solenoid valve as follows:
- during starting, the solenoid valve remains closed, preventing the fuel vapours from enriching the mix-
ture; this condition persists until the engine coolant reaches 25°C;
- with the engine at operating temperature, the control unit operates the solenoid valve in duty-cycle in
order to control the quantity of fuel vapours sent to the intake, according to the engine speed and load
conditions.
In the following operating conditions:
- butterfly in closed position,
- engine speed below 1250 rpm,
- engine load below a pre-set level
the operation of the solenoid valve is disabled, keeping it in the closed position.
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