Fiat 1996 Brava Service Manual page 309

Bravo 10»
98 range
20v
Engine
Fuel system
10.
These values have been obtained experimentally, by means of a long series of practical tests carried out
on prototypes at the engine test bench, to identify the advances which give the best compromise be­
tween the conflicting requirements of maximum power and a reduction in fuel consumption and harmful
exhaust emissions.
These optimum advances have then been memorized in the system control unit. During the operation of
the engine, the control unit is constantly informed of the (engine) speed and load conditions and on this
basis it "selects" the optimum advance from its memory to strike the spark at the spark plug for the cylin­
der in the explosion stroke with the optimum advance.
In addition, the control unit corrects this value, depending on other factors such as the engine coolant
temperature, intake air temperature, detonation and butterfly valve position, so that the ignition point is
always optimum.
The information required by the control unit to operate the single coils is transmitted by means of electri­
cal signals sent by the following sensors:
a. An rpm sensor which produces a single phase alternating signal whose frequency indicates the en­
gine speed.
b. An air f l o w meter with a temperature sensor which, on the basis of the quantity/temperature of the
air drawn in by the engine, transforms these figures into electrical signals, sending them to the elec­
tronic control unit.
c. T w o detonation sensors which, located in the upper part of the cylinder block/crankcase, one
between cylinders 1 and 2 and the other between cylinders 4 and 5, respectively, allow the control
unit to recognize the cylinder where detonation (or the onset of detonation) is taking place and only
correct the ignition advance for the spark plug of the cylinder concerned.
d. An accelerator pedal potentiometer which transforms the angular value of the actual pedal into
an electrical signal allowing the control unit to recognize minimum, partial and full load conditions.
Functions of the injection/ignition system
In addition to electronically controlling the moment of ignitionand the air flow rate during idling, in or­
der to allow the engine to run smoothly when the ambient parameters and loads applied vary, the con­
trol unit should control and manage the injection in such a way that the stoichiometric (air/fuel) ratio is
always within the optimum value.
The electronic control unit establishes the operating «time» for the injectors using a relatively simple rule
which can be summarized as follows.
Taking the physical properties of the fuel (viscosity and density) and the difference in pressure between
the pressure of the fuel and the pressure in the inlet manifolds as constant, the quantity of fuel to be in­
jected only depends on the injector «opening time».
The injection/ignition system basically carries out the following functions:
adjustment of injection time;
adjustment of ignition advance;
check on cold starting;
check on the enrichment during acceleration;
fuel cut-off during deceleration;
check on engine idle speed;
restriction of the maximum engine speed;
control of combustion through the Lambda
sensor;
fuel vapour recovery;
- control of the detonation;
- control of the phase transformer;
- check on the inlet manifold
- self-adjustment of the system;
- autodiagnosis;
- connection with the engine immobilizer de­
vice (Fiat CODE);
- management of the climate control system;
- management of the radiator fans.
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