Fiat 1995 Brava, Service Manual

Page: 108 / 544

Engine
Bravo-Brava
iffyix,
Fuel system
10.
Over-run and cut-off
During over-run, the mixture must be made more lean to reduce fuel consumption and polluting emis-
sion levels (HC + C O ) .
To achieve this aim, the control unit contains a function known as fuel C U T - O F F that is dependent
upon the closure of contact (1) in the idle control motor at a given coolant temperature and rpm.
The first two conditions necessary for activating the C U T - O F F function are:
- coolant temperature in excess of 40° C,
- engine rpm in excess of 1800/min.
If the above over-run conditions exist, idle contact (1 - throttle closed) earths terminal 3 of the control
unit, which cuts off fuel injection via terminal 21.
In addition to fuel cut-off, the control unit activates a specific ignition curve with "over-run" advance
settings.
Fuel injection cut-off and specific advance curves remain in operation until the engine reaches a speed
of 1500/min. Below this speed, injection pulses are activated to prevent the engine stalling.
When injection is restored, the control unit implements a fuel enrichment strategy in order to re-form the
fuel film on the manifold and thus optimise engine efficiency.
6 Publication no. 506.670