Fuel Vapour Recovery; Control Of The Phase Transformer; Check On The Inlet Manifold - Fiat Bravo Service Manual

Engine
Fuel system
10.

Fuel vapour recovery

The fuel vapours (pollutant according to regulations) are sent to an active charcoal filter and from these
to the engine where they are burnt; this takes place by means of a solenoid valve which is only operated
by the control unit w h e n the engine load condition is such as to allow correct combustion w i t h o u t the
operation of the engine being "disturbed": in effect, the control unit compensates for this quantity of i n -
coming petrol by reducing the supply to the injectors.
Control of the detonation
This function is designed to detect the presence of the phenomenon of detonation (engine knock), by
processing the signal coming from the appropriate sensors. The control unit continuously compares the
signals coming from the sensors w i t h a threshold value w h i c h 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 detona-
tion) and reduces the ignition advance (by 3° up to a maximum of about 9°), until the phenomenon dis-
appears. Later on, the advance is gradually restored to the basic value.
In acceleration conditions, a higher threshold is used, to take into account the increased engine noise u n -
der these circumstances. The detonation control strategy is also equipped w i t h a self-adjustment function
which memorizes the reductions in the advance w h i c h are continuously repeated to adpat the map to the
different conditions in which the engine finds itself.
Control of the p h a s e t r a n s f o r m e r
1. Transformer in O N position
2. Accelerator pedal fully depressed
3. Maximum speed limit
Obviously the control of the phase transformer operates w i t h a hysteresis field, in other words the level
at which the solenoid valve is activated is always higher than the level at w h i c h is it deactivated; this is
designed to avoid balance conditions and too rapid a succession from one timing diagram to another
with obvious operating problems.

Check on the inlet manifold

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 a configuration with long ducts.
6
The control unit controls the solenoid valve for
the phase transformer hydraulic actuator (fitted
on the camshaft, inlet side) by means of a relay.
The transformer has t w o operating positions:
A. OFF position (power, reduced engine loads
and idling), corresponding to the normal
camshaft value;
B. ON position (torque), corresponding to an
18° crankshaft advance for the camshaft.
The transformer, normally in the OFF position, is
switchedto the ON position according to the
engine load and rotation speed, as illustrated in
the diagram.
In any case, the ON position is only enabled for
coolant temperatures above 40°C.
Bravo @ 2 ,
0
98 range
Print no. 506.670/16