Injection Management - Fiat Bravo Service Manual

Engine
Fuel system
10.

INJECTION MANAGEMENT

The E C U receives information on rpm (n) and throttle valve opening (alpha) and is then able to identify
base pulse constant (ti) within a specific map.
Under various different engine service conditions, injector opening times are optimised by correcting
times (in accordance with changing conditions) of: coolant temperature (1), air temperature (2) and
signal received from lambda probe (3). Injection is synchronous at all times, i.e. timed to coincide with
the moment of ignition.
The E C U uses specially selected maps to keep fuel mixture concentration close to stoichiometric levels
(14.7 parts air to 1 part petrol).
To maintain this ratio constant, the ECU uses two different modes for the control of injector opening.
The first mode is synchronous operation, where the injector is opened whenever a high tension
pulse is sent to the spark plugs (graph A ) .
The second control mode is asynchronous operation, where the ECU controls injector opening re-
gardless of the number of high tension pulses sent to the spark plugs (graph B ) .
This occurs because under certain conditions (with base pulse constants too short, ^ 1.4 milliseconds)
mechcanical inertia characteristics (hysteresis) of the injector do not permit proper opening and closure.
For this reason, a specific strategy must be adopted to suit mechanical injector properties.
2
Bravo-Brava
Publication
P4A02AJ01
no. 506.670