Fiat 1996 Brava Service Manual page 352

Bravo-Brava i f ^ Engine
98 range Fuel system
10.
Controlling the quantity of fuel injected
On the basis of the signals coming from the accelerator pedal potentiometer, the flow meter and the rpm
sensor, the control unit operates the fuel pressure regulator and the injectors, as appropriate.
The timing and consequently the injection sequennce, is determined by the starting of the engine using
the signals coming from the rpm sensor and the timing sensor (synchronization stage); later, the injec­
tion timing is implemented using only the rpm sensor signal and the injection sequence 1 -3-4-2.
The control unit inhibits the injection in the following cases:
- fuel pressure value above 1500 bar;
- fuel pressure value below 120 bar;
- engine speed above 6000 rpm.
At operating temperature the maximum duration of the injection (injector opening time) is 1500 ns,
whilst during starting it can reach 3000 ns.
Control of injection advance
The electronic control unit determines the injection advance mainly on the basis of the quantity of fuel to
be injected.
Later on, the injection advance is corrected according to the temperature of the engine coolant and the
speed in order to compensate, whilst the engine is warming up, for the increase in the ignition delay due
to the low temperatures in the combustion chambers.
Control of injection pressure
This check is esepcailly important because the injection pressure affects the following parameters:
- the quantity of fuel introduced into the cylinders for the duration of the injection time;
- the atomization of the fuel injected;
- the penetration of the jet;
- the delay between the electrical operation of the injector and the effective start and end of injection.
The above mentioned parameters have a considerable effecton the behaviour of the engine, especially as
far as the power supplied, exhaust emissions, noise and driveability are concerned.
On basis of the engine load, the injection control unit operates the pressure regulator to ensure a line
pressure which is always optimum.
With the engine cold, the injection pressure is corrected on the basis of the engine coolant temperature
and speed in order to satisfy the engine requirements at different operating temperatures.
Control of the auxiliary electric fuel pump
The auxiliary electric fuel pump, immersed in the tank, is supplied by the injection control unit via a relay
when the ignition key is in the ON position.
The supply to the electric pump is inhibited when one of the following conditions occurs:
- after the ignition key has been in the ON position for a certain length of time and the engine has not
been started up;
- if the inertia switch has been operated.
Control of injection during deceleration (cut-off)
The cut-off strategy is implemented when the injection control unit receives the information from the
potentiometer that the accelerator pedal is released.
Under these circumstances, the control unit removes the supply to the injectors and reactivates before
the idle speed is reached.
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