Fiat Bravo Service Manual page 354

Bravo $
2 0 v
Engine
Fuel system
10.
SYSTEM M A N A G E M E N T STRATEGIES
Adjustment of the injection times
Digital technology has made it possible to obtain optimum fuel consumption and performance by using
programmed maps, stored inside the electronic control unit memory, dependent on the engine speed
and load conditions.
The control unit controls the injectors with extreme speed and precision, calculating the opening time
on the basis of the load on the engine (number of revs and air flow rate) also taking into account the
battery voltage and the temperature of the engine coolant.
The injection is sequential and timed for each cylinder (the moment of injection is not simultaneous for
all the cylinders) and takes place corresponding to the optimum injection point.
Adjustment of ignition advances
Thanks to a map memorized inside the electronic control unit it is capable of calculating the advance ac­
cording to the engine load (minimum, partial, full, on the basis of the number of revs and air flow rate),
the temperature of the intake air and the temperature of the engine coolant.
It is possible to delay the ignition selectively for the cylinder requiring it, which can be recognized via the
combination of the values recorded by the detonation and cam angle sensors.
Checking cold starting
Under these circumstances there is a natural weakening of the mixture as a result of the poor turbulence of
the particles of fuel at low temperatures, reduced evaporation and condensation on the inner walls of the
inlet manifold, all of it exacerbated by the increased viscosity of the lubrication oil.
The electronic control unit recognizes this condition and corrects the injection time on the basis of the
coolant temperature signal, the temperature of the intake air, the battery voltage and the engine speed.
The ignition advance is only dependent on the number of revs and the temperature of the engine
coolant.
During starting the control unit controls an initial simultaneous injection for all the injectors (full-group
injection) and after the reference on the flywheel is recognized, it switches to the normal sequential
timed operation.
Whilst the engine is warming up, the electronic control unit controls the idle speed actuator which de­
termines the quantity of air required to ensure that the engine does not cut out.
The rotation speed is made to decrease proportionally as the temperature increases until the nominal
value is obtained when the engine has reached operating temperature.
Checking acceleration enrichment
When there is a request for acceleration, if the air flow meter signal variation exceeds a pre-set increase,
the control unit not only adjusts the injection to the new requirements, but also increases it further
through rapidly reaching the speed required.
When approaching the pre-set speed, the injection increase is gradually eliminated.
NOTE The request for acceleration is also detected by the potentiometer on the butterfly; this makes it
possible to ensure optimum running if there is a failure in the air flow meter until a Service Deal­
er can be reached.
Fuel cut off during deceleration
The fuel cut off during deceleration is the modified type.
When the closed butterfly condition is recognized and the engine speed is greater than 1700 rpm (for
engine speeds below 1700 rpm the cut off function is not operational to maintain optimum "driveabili-
ty") the injection of fuel is deactivated.
With no fuel supply, the engine speed starts to decrease more or less quickly depending on the vehicle
driving conditions.
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