Fiat 1998 Marea Weekend, Service Manual

Page: 222 / 846

Engine
Marea- Marea Weekend ©
Fuel system
99 range
10.
Starting and operation when cold
During cold starting the injection is managed simultaneously (full-group), i.e. not phased: this situation
persists until a certain coolant temperature is reached (about 0°C), after which the management becomes
phased.
The injection time whilst the engine is being driven by the starter motor is determined by a special map
according to the temperature of the coolant: when the engine is started up, the calculation returns to the
normal speed/load map.
During operation when cold, since there is a natural weakening of the mixture as a result of the reduced
evaporation and the strong condensation of the fuel on the internal walls of the inlet manifold, the "basic"
injection time is increased by a multiplication coefficient which depends on the temperature and speed of
the engine.
Operation in full load conditions
This strategy is enabled when the butterfly exceeds a certain threshold which depends, in turn, on the en-
gine speed.
The injection time in this situation is determined by a special map which depends on the engine load and
speed conditions.
Operation in acceleration and deceleration conditions
The acceleration or deceleration situation is interpreted by the system as a transition stage between two
conditions, departure and arrival: this transition can be positive (acceleration) or negative (deceleration).
The transition management strategy is very complex, having to take a large number of factors into account.
In general, the injection time is increased for positive transitions and reduced for negative ones.
The extent of the correction basically depends on the variation in the engine load: however, the movement
speed of the butterfly, the engine speed, the gear engaged (taken from the ratio between the engine speed
and the vehicle speed) and the temperature of the engine (coolant and intake air) all have an effect and
are interconnected in different ways.
The "basic" injection time is multiplied by a coefficient, in turn the sum of two coefficients: the first takes
into account the temperature of the engine and the 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 control
unit reopens the injector (extra pulse) in order to compensate the mixture strength extremely quickly: the
subsequent injections are, on the other hand, already increased on the basis of the coefficients mentioned
previously.
Operation in cut-off conditions
The control unit enables the cut-off strategies 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 minimum
position (butterfly potentiometer signal): it is disabled when the engine is cold to prevent driveability
problems.
The engine supply is enabled again when the butterfly is no longer closed or when the engine speed goes
below a level which depends on the coolant temperature.
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