System Managemenes Strategis; Adjustment Of The Injection Time; Adjustment Of Ignition Advance; Check On The Cold Starting - Fiat Bravo Service Manual

Engine
Fuel system
10.

Adjustment of the injection time

Digital technology has made it possible to achieve optimum fuel economy and performance using pro-
grammed maps, stored inside the electronic control unit memory, dependent of the engine speed and
load.
The control unit controls the injectors with great speed and precision, calculating the opening time on
the basis of the engine load (speed and air f l o w rate), also taking into account the battery voltage and
the temperature of the engine coolant.
The injection is sequential and phased for each cylinder (the moment of injection is not simultaneous for
all the cylinders) and takes place at the optimum injection point.

Adjustment of ignition advance

Thanks to a map stored in its memory, the control unit is capable of calculating the advance according to
the engine load conditions (minimum, partial, full according to the engine speed and air f l o w rate), the
temperature of the intake air and the temperature of the engine coolant.
It is possible to selectively delay the ignition at the cylinders required, recognized by means of the c o m -
bination of values recorded by the detonation and cam angle sensors.

Check on the cold starting

Under these circumstances there is a natural weakening of the mixture as a result of the poor turbulence of
the particles of fuel at l o w temperatures, the reduced evaporation and the condensation on the internal
walls of the inlet manifold, all of which is exacerbated by the increased viscosity of the lubricant oil.
The electronic control unit recognizes this condition and corrects the injection time on the basis of the sig-
nal for the temperature of the coolant, the temperature of the intake air, the battery voltage and the engine
speed.
The ignition advance depends exclusively on the engine speed and the temperature of the engine
coolant.
During cold starting the control unit controls an initial simultaneous (full-group) injection for all the i n -
jectors and after recognition of the reference on the flywheel, it switches to the normal, sequential,
phased operation. Starting when warm takes place straightaway in a phased sequential manner.
Check on the enrichment of the mixture during acceleration
The control unit detects the acceleration request from the signal supplied by the accelerator pedal po-
tentiometer and, as a result, increases the injection times and modifies the opening of the butterfly valve
to reach the desired engine speed quickly.
If in response to an acceleration request, the variation in the signal supplied by the air f l o w meter ex-
ceeds a pre-set increase, the control unit not only adapts the injection to the new requirements, but also
further increases it for several seconds to improve the responsiveness.
Fuel cut-off during deceleration
When the accelerator pedal is released and beyond a pre-set engine speed threshold, the injection c o n -
trol unit cuts off the supply to the injectors.
With no supply, the engine speed starts to decrease at a rate w h i c h depends on the vehicle driving c o n -
ditions.
Before reaching the idle speed, the dynamics of the engine speed dcrease are verified.
If they are above a certain value, the fuel supply is partly reactivated on the basis of a logic w h i c h i n -
volves the "gentle accompaniment" of the engine during idling.
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S Y S T E M M A N A G E M E N T S T R A T E G I E S
Bravo ft 20v
98 range
Print no. 506.670/16