Fiat 1998 Marea Weekend, Руководство по обслуживанию

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Engine
Fuel system
Marea- Marea Weekend ft
99 range
10.
Fuel vapour recovery
The fuel vapours (pollutant according to the regulations) are sent to an active charcoal filter and from
there to the engine where they are burnt; this takes place by means of a solenoid valve which is only op-
erated by the control unit when the engine load conditions allow correct combustion without the opera-
tion of the engine being "disturbed": in effect, the control unit compensates for this quantity of petrol en-
tering with a reduction in the injector supply.
Detonation control
This function has the task of detecting the presence of detonation (engine knock) by processing the signal
coming from the sensors. The control unit continously compares the signals coming from the sensors with
a set level which is, in turn constantly updated to take into account background noise and the ageing of
the engine.
The control unit is therefore capable of detecting the presence of detonation (or the onset of detonation)
and reduces the ignition advance (from 3° up to a maximum of about 9°) until the phenomenon disap-
pears. Later on, the advance is gradually restored to the basic value.
In acceleration conditions, a higher level is used to take into account the increased noise of the engine in
these circumstances. The detonation control strategy is also equipped with a self-adjustment function
which memorizes the reductions in the advance which are continuously repeated to adapt the map to the
various conditions in which the engine finds itself.
Phase transformer control
The control unit controls the phase transformer
hydraulic actuator solenoid valve (fitted on the
inlet side camshaft) via a relay.
There are two operating positions for the trans-
former:
A. OFF position (power, reduced engine loads
and idling), corresponding to the normal cam-
shaft fitting value;
B. ON position (torque), corresponding to an
18\272 crankshaft advance of the camshaft.
The transformer, usually in the OFF position, is
switched to the ON position depending on the
engine load and speed conditions, as illustrated
in the diagram.
In any case, the ON position is only enabled at
coolant temperatures above 40°C.
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RpM
4A06LJ01
1. Transformer in ON position
2. Accelerator pedal fully depressed
3. Maximum speed restriction
Obviously the phase transformer control operates within a hysteresis range, i.e. the level for activating the
solenoid valve is always higher than that for deactivating it; this is designed to prevent balanced condi-
tions and too rapid a progression from one timing diagram to another with obvious operating problems.
Inlet manifold control
The control unit controls the geometry of the inlet manifolds to optimize the quantity of air drawn in by
the engine.
The control unit selects short ducts for speeds above 4500 RPM and high engine loads.
In other engine operating conditions, the control unit selects the long duct configuration.
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