Fiat 1996 Brava Service Manual page 419

Bravo-Brava ^ ** Engine
'98 range Fuel system
10.
Operation in deceleration
During this stage of use of the engine, two strategies are superimposed:
1. A negative transient strategy for maintaining a stoichiometric quantity of fuel supplied to the engine
(less pollution).
This stage is recognized by the control unit when the throttle potentiometer signal changes from a
high voltage value to a lower value.
2. A strategy for soft accompaniment at low speed (dash-pot) to attenuate the variation of delivered
torque (less engine braking).
When the potentiometer signal indicates closed throttle and the idle speed is high, the control unit,
acting on the engine idle speed actuator, gradually decreases the air flow passing through the b y ­
pass.
Barometric correction
The atmospheric pressure varies in accordance with altitude, causing a variation in the volumetric effi­
ciency such as to require correction of the basic strength (injection time).
The correction of the injection time will depend on the variation in altitude and will be updated automat­
ically by the electronic control unit whenever the engine is switched off and under particular conditions
of throttle valve position and engine speed (typically at low rpm and throttle wide open) (dynamc ad­
justment of barometric correction).
Operation in cut-off
The fuel cut-off strategy is effected when the control unit recognizes the throttle valve in idle position
(signal from throttle potentiometer) and the engine idle speed exceeds 1350 rpm (1750 rpm for version
with automatic transmission). The control unit enables the cut-off only when the engine temperature
exceeds 0° C.
The recognition of the throttle valve in a non-closed position of the engine idle speed below 1270 rpm
(1650 rpm for version with automatic transmission) re-enables the fuel supply to the engine.
For very high engine speeds, cut-off is also effected when the throttle valve is not fully closed, but with
particularly low pressure in the inlet manifold (partial cut-off).
Version with manual
gearbox
1. 1350 rpm
2. 1270 rpm
Version with automatic
transmission
1. 1750 rpm
2. 1650 rpm
A. entry into cut-off
B. exit from cut-off
Rpm.
1
2
N . A \ v
80 °C
TEMP. H20
Copyright Fiat Auto
1