Fiat 1998 Marea Weekend, Service Manual

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Engine
Marea- Marea Weekend
9
»°9> ™
Fuel system 99 range
10.
Control of idle speed
According to the signals coming from the rpm sensor and the engine coolant temperature sensor, the in-
jection control unit operates the pressure regulator and alters the operating times for the injectors to keep
the idle speed constantly stable.
In certain conditions, the control unit also takes into account the battery voltage when controlling the idle
speed.
Maximum speed restriction control
According to the number of revs, the injection control unit limits the maximum speed through two types
of intervention:
- as the maximum speed is approached, it decreases the quantity of fuel injected, reducing the line pres-
sure;
- when 6000 rpm is exceeded it inhibits the operation fo the injectors.
Maximum torque restriction control
According to the engine speed, the injection control unit calculuat.es the torque limit and maximum per-
missible fumes parameters using pre-defined maps in its memory.
It therefore corrects the above parameters with data on the engine coolant temperature and vehicle speed
and uses the figures obtained in this way to meter the quantity of fuel to be injected acting on the pres-
sure regulator and the injectors.
Fuel temperature control
The injection control unit is constantly informed of the temperature of the fuel by the snsor on the return
manifold.
If the temperature of the fuel exceeds a certain value (about 110 °C), the control unit reduces the line
pressure acting on the pressure regulator and leaving the injection times unaltered.
Engine coolant temperature control
The injection control unit is constantly informed of the temperature of the engine coolant by the sensor on
the thermostat.
If the temperature of the engine coolant exceeds certain values, the control unit implements the following
strategies:
- it reduces the quantity of fuel injected, acting on the pressure regulator and the injectors (power reduc-
tion);
- it operates the engine radiator cooling ran.
Heater plugs control
The injection control unit controls the operation of the heater plugs control unit so that the temperature in
the combustion chambers facilitates the self-ignition of the fuel and makes starting easier.
In effect, the injection control unit controls the operation of the heater plugs control unit for a given pe-
riod of time both before (pre-heating) and after (post-heating) the engine is started and also controls the
warning light in the instrument panel.
The pre-heating and post-heating times, plus how long the heater plugs warning light remains on, depend
on the temperature of the engine coolant.
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