Management Of Fuel Injection - Fiat Bravo Service Manual

Bravo-Brava
'98 range
The management strategies ensure the best ignition advance and fuel delivery, thus providing the cor-
rect mixture strength at all times as the engine load and environmental conditions vary.
The system management strategies are basically as follows:

-management of fuel injection;

-management of ignition;
-management of engine starting block function (Fiat CODE);
-management of radiator fan;
-management of engine idle control;
-management of fuel vapour recirculation;
-management of fault diagnosis;
-management of climate control system.
M A N A G E M E N T OF F U E L I N J E C T I O N
The fuel injection management strategy aims to supply to the engine the correct quantity of fuel at the
required instant, in accordance with the engine's operating conditions.
The fuel injection-ignition uses a "SPEED DENSITY-LAMB DA" indirect measuring system, w h i c h mea-
sures angular speed of rotation, density of intake air and mixture strength control (feedback control).
In practice, the system uses the ENGINE SPEED (rpm) and AIR DENSITY (pressure and temperature)
data to measure the quantity of air drawn in by the engine.
The quantity of air drawn in by each cylinder for each engine cycle depends not only on the density of
the air drawn in, but also on the unit cylinder capacity and the volumetric efficiency.
Air density is the density of the air drawn in by the engine and calculated in accordance w i t h the abso-
lute pressure and temperature, both measured in the inlet manifold.
Volumetric efficiency is the parameter relating to the cylinder fill coefficient measured in accordance
w i t h experimental tests conducted on the engine throughout its operating range, and subsequently
stored in the electronic control unit's memory.
After establishing the quantity of air drawn in, the system must provide the quantity of fuel in accor-
dance w i t h the desired mixture strength.
The end-of-injection or delivery timing pulse is contained in a map stored in the control unit's memory,
and varies depending on the engine speed and pressure in the inlet manifold. In effect these are process-
ing operations carried out by the control unit to control the sequential opening and timing of the four in-
jectors, one per cylinder, for the length of time strictly necessary for forming an air-petrol mixture as
close as possible to the stoichiometric ratio.
The fuel is injected directly in the manifold near the inlet valves at a differential pressure of about 3 bar.
The speed (rpm) and air density (pressure and temperature) are used to measure the quantity of intake
air; when this has been determined, the quantity of fuel is metered in accordance w i t h the desired mix-
ture strength. The other sensors present in the system (coolant temperature, throttle valve position, bat-
tery voltage, etc.) enable the electronic control unit to correct the basic strategy for all the particular op-
erating conditions of the engine.
Making the air-fuel ratio fluctuate around stoichiometric values is the essential condition for both cor-
rect and long-lasting operation of the catalytic converter, and for reducing polluting emissions.
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16v
E n g i n e
Fuel system
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