Fiat Bravo Service Manual page 161

Engine Bravo-Brava @|i
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v
Fuel system
10.
ENGINE IDLE CONTROL
The main aim of this strategy is to maintain engine speed at around the mapped setting (warm engine:
850 rpm): the position assumed by the actuator is dependent on engine conditions/rpm and vehicle
speed.
Start-up stage
When the key is inserted, the actuator takes up a position dependent on engine temperature and battery
voltage (open-loop position).
Warming-up stage
The rpm is mainly corrected on the basis of coolant temperature.
With the engine warm, idle management is dependent upon the signal from the rpm sensor. The ECU in­
troduces sustained idle when external loads are activated.
Deceleration stage
When the accelerator is released when the car is not idling, the ECU governs the actuator (step motor)
by measn of special delivery curve (dash-pot curve), i.e. delays the return of the plunger to its housing to
bring about a reduction in engine braking effect.
FUEL VAPOUR RECIRCULATION MANAGEMENT
The strategy controls vapour cut-off solenoid position as follows:
- during start-up, the solenoid remains closed to prevent fuel vapours enriching the mixture excessively.
This condition persists until coolant temperature reaches 65° C;
- with the engine warm, the ECU sends the solenoid a square wave signal (duty-cycle control) which
modulates opening.
In this way, the ECU controls the amount of fuel vapour directed to the intake, thus avoiding sub­
stantial changes in mixture concentration.
Under the following operation conditions:
- throttle valve closed
- speed less than 1500 rpm
- intake manifold pressure less than a lower threshold calculated by the ECU in accordance with rpm
level
solenoid control is inhibited with the same closure position maintained. This makes engine operation
more efficient.
TEST MANAGEMENT
Full injection-ignition system electronic testing can be achieved by connecting a FIAT/LANCIA
TESTER to the test socket.
The system is also equipped with a self-diagnostic function which recognises, memorises and indicates
any faults.
If sensors or actuators are found to be faulty, signal reconstruction strategies are immediately activated
(recovery) so that the engine is able to operate at an acceptable level without affecting function. The car
can then be driven to a service point for the necessary repairs.
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Publication no. 506.670