Operation When Cold; Connection With The Automatic Transmission; Operation At Full Load - Fiat Bravo Service Manual

Engine
Fuel system
10.

Operation when cold

Under these conditions, the mixture is naturally weakened by poor turbulence of the fuel particles at l o w
temperature, low evaporation and high condensation on the inner walls of the inlet manifold, all height-
ened by the greater viscosity of the lubricating oil which, as is known, at low temperature increases the
resistance to rolling of the engine's mechanical components.
The electronic control unit recognizes this condition and corrects the fuel injection time on the basis of
the coolant temperature signal.
Consequently:
- At very low temperatures, the fuel injector remains open for longer (tj) graph ( b ) , w i t h a low air/petrol
ratio (rich mixtures).
- The more the engine temperature increases, the shorter the fuel injector's opening time, (tj) graph (a),
consequently the higher the air/petrol ratio (poor mixtures).
During the engine warming-up period, the electronic control unit also drives the stepper motor w h i c h
determines the quantity of air necessary for ensuring the engine's self-sufficient speed.
The idle speed is decreased proportionally as the temperature increases until the nominal value is o b -
tained (850 ± 30 rpm) when the engine is up to temperature. The electronic control unit, by driving the
stepper motor, keeps the idle speed constant even when the electrical and mechanical loads vary.

Connection with the automatic transmission

The control unit adjusts the engine idle speed in accordance w i t h the load w h i c h occurs w h e n the selec-
tor lever is moved to a gear ratio and transmits to the automatic transmission control unit information re-
lating to the reduction in torque (pin 36), coolant temperature (pin 5) and throttle valve position (pin
16).
The control unit reduces the torque delivered by the engine (mainly by intervening on the ignition a d -
vance) during gear changes, w h e n it receives an appropriate signal from the automatic transmission
control unit (pin 4 9 ) .

Operation at full load

Under full load conditions, the basic injection time must be increased to obtain the maximum power de-
livered by the engine.
The full load condition is detected by the control unit via values supplied by the throttle position and ab-
solute pressure sensors.
On the basis of this information, the control unit makes the appropriate correction, increasing the basic
injection time.
6
Bravo-Brava ft 1 *
'98 range
P4A06IJ01
Publication no. 506.670/14