Management Of Engine Idle Control; Management Of Fuel Vapour Recirculation; Management Of Fault Diagnosis; Starting Stage - Fiat Bravo Service Manual

Bravo-Brava
'98 range
M A N A G E M E N T O F ENGINE I D L E CONTROL
The general aim of the strategy is to keep the engine idle speed around the value stored in memory (hot
engine: 850 rpm): the position assumed by the actuator depends on the engine conditions:

Starting stage

When the ignition is switched on, the actuator assumes a position in relation to the engine coolant tem-
perature and battery voltage (open loop position).
W a r m i n g - u p s t a g e
The rpm is corrected mainly in relation to the coolant temperature.
With the engine up to temperature, depends on the signal coming from the engine rpm sensor; w h e n ex-
ternal loads are switched on, the control unit manages the steady idle.
Deceleration stage
Under overrun conditions above idle speed, the control unit controls the position of the engine idle ac-
tuator by means of a particular f l o w curve (curva di dash-pot), i.e. it slows d o w n the return of the shutter
towards its sealing seat, thus optimizing the engine braking effect.
M A N A G E M E N T O F F U E L VAPOUR R E C I R C U L A T I O N
The strategy controls the position of the cut-off solenoid as follows:
- during starting, the solenoid remains closed, preventing the fuel vapours from making the mixture ex-
cessively rich; this condition remains until the coolant reaches a temperature of 65° C;
- when the engine is up to temperature, the electronic control unit sends the solenoid a square-wave
signal (duty cycle control) w h i c h modulates its opening.
In this way the control unit controls the quantity of fuel vapours sent to the inlet manifold, thus prevent-
ing significant changes in mixture strength.
In the operating conditions listed below:
- throttle valve in closed position
- speed below 1500 rpm
- pressure in inlet manifold below a limit value calculated by the control unit in accordance w i t h the rpm
solenoid control is inhibited, and the solenoid is kept in the closed position; this is t o improve the en-
gine's operation.
M A N A G E M E N T O F FAULT D I A G N O S I S
A complete electronic diagnosis of the fuel injection-ignition is obtained by connecting the appropriate
equipment (EXAMINER or SDC station) to the diagnostic socket.
The system also comprises a self-test function which recognizes, stores in memorey and indicates any
faults.
If a fault is detected on sensors or actuators, signal reconstruction (recovery) strategies are immediately
activated to ensure engine operation at an acceptable level without impairing its functionality. It is thus
possible to drive the vehicle to a repair garage for the appropriate operations.
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16v
E n g i n e
Fuel system
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