Fiat 1996 Brava Service Manual page 259

Engine Bravo-Brava j_pi i *
Fuel system 98 range
10.
Starting and operation when cold
During cold starting the management of the injection is simultaneous (full-group), i.e. not phased: this
situation persists until the coolant reaches a certain temperature (about 0°C), after which the manage­
ment becomes phased.
Whist the starter motor is working the injection time is determined by a special map and depends on the
temperature of the coolant: once the engine has been startedup, the regular speed-load map is used for
the calculations.
During operation when cold, since the mixture is naturally weakened as a result of the reduced evapora­
tion and the strong condensation of the fuel on the internal walls of the inlet manifold, the "basic" injec­
tion time "is increased by a multiplication coefficient which depends on the engine temperature and
speed.
Operation in full load conditions
The strategy is enabled when the butterfly exceeds a certain level, which, in turn, depends on the engine
speed.
In this situation the injection time is determined by a special map which depends on the engine load and
speed conditions.
Operation in acceleration and deceleration conditions
The acceleration and deceleration conditions are interpreted by the system as a trasition stage between
two conditions, setting off and arriving: this transition can be positive (acceleration) or negative (decel­
eration).
The transition management strategy is very complex, having to take a large number of factors into ac­
count.
In general, the injection time is increased for positive transitions and reduced for negative ones.
The extent of the correct basically depends on the variation in the engine load: however, other factors
such as the speed of movement of the butterfly, the engine speed, the gear engaged (obtained from the
ratio between the engine speed and the vehicle speed), the temperature of the engine (coolant and in­
take air) which are interconnected also have an impact.
The "basic" injection time is multiplied by a coefficient which is, in turn, the sum of two coefficients: the
first takes into account the temperature of the engine and opening speed of the accelerator butterfly; the
second depends on the engine rotation speed.
In particular, if the increase in the injection time is feasible at an injector which has just closed, the con­
trol unit reopens the injector (extra pulse), in order to compensate for the mixture strength extremely
quickly: thcsubsequent injections are already increased on the basis of the coefficients mentioned pre­
viously.
Operation in cut off conditions
The control unit enables the cut-off strategy when the temperature of the engine exceeds a certain level.
The cut-off strategy is implemented when the control unit recognizes that the butterfly is in the mini­
mum position (signal from the butterfly potentiometer): it is disabled when the engine is cold to avoid
driveability problems.
The engine supply is re-enabled when the butterfly is recognized to be in a non closed position or when
the engine speed goes below a level which depends on the coolant temperature.
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Print no. 506.670/16