Fiat 1998 Marea Weekend, Service Manual

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Engine
Marea- Marea Weekend &
Fuel system
99 range
10.
MANAGEMENT OF THE ENGINE IDLE SPEED CONTROL
The general objective of the strategy is to keep the engine speed around the value memorized (engine
warm: 800 rpm); the position of the butterfly depends on the engine conditions and speed and the vehicle
speed.
When the key is inserted, the butterfly assumes a position which depends on the temperature of the en-
gine and the battery voltage (open loop position).
- Engine running and accelerator pedal released.
The engine speed varies according to the temperature of the engine and is kept constant close to this
value by altering the position of the butterfly to compensate for any fluctuations in the speed.
This takes place, in particular, when external loads are applied (power steering, heated rear windscreen,
etc.).
If the fans and the air conditioning is switched on, both managed by the control unit and the power as-
sisted steering reaches the end of travel position, signalled by a switch, the strategy manages the butterfly
in advance of the load being applied.
- Normal driving.
Under these circumstances the actuator is in the open loop position.
- Deceleration.
In release conditions outside of idling, the control unit controls the position of the butterfly through a par-
ticular flow rate curve (dash-pot curve), i.e. it slows down the return of the butterfly to the closed position
thereby producing a reduction in the braking effect of the engine.
In addition, if the vehicle is decelerating, the information concerning its speed, correlated to that of the
engine speed, allows the optimum management of the dash-pot effect adapting it to the gear engaged.
MANAGEMENT OF THE ACTIVE CHARCOAL FILTER
This strategy controls the position of the charcoal solenoid valve in the following way:
- during starting the solenoid valve remains closed, preventing the fuel vapours from enriching the mix-
ture;
- after cold starting, the solenoid valve remains closed for the entire time the engine is warming up;
- with the engine warm, the control unit operates the solenoid valve in duty-cycle to control the quantity
of fuel vapours sent to the inlet (scavenging of the charcoal filter) according to the engine speed and
load. In particular, the system alternates periods of scavenging with periods free from scavenging: during
the latter, the self-adjustment strategy, which is disabled during the scavenging, finds itself enabled;
the solenoid valve remains closed in cut-off conditions.
12 Print n° 506.763/14
- Starting.