Fiat 1998 Marea Weekend, Service Manual

Page: 395 / 846

Marea-Mates Weekend®™®™
99 range
Engine
Fuel system
10.
Checking quantity of fuel injected
According to the signals coming from the accelerator pedal potentiometer, the flow meter and the rpm
sensor, the control unit controls the fuel pressure regulator and the injectors.
The injection timing and phasing is determined by the starting of the engine using the signals coming
from the rpm sensor and the timing sensor (synchronization phase); later, the injection timing is imple-
mented using only the rpm signal and with the injection sequence 1-3-4-2 for the 1910 JTD version and
1 -2-4-5-3 for the 2387 JTD version.
The control unit inhibits the injection in the following cases:
fuel pressure value above 1500 bar;
fuel pressure value below 120 bar;
engine speed above 6000 rpm.
At operating temperature the maximum duration of the injection (opening time of the injector) is 1500 ns,
whilst during starting it can reach 3000 ns.
Injection advance check
The electronic control unit determines the injection advance mainly on the basis of the quantity of fuel to
be injected.
Later on, the injection advance is corrected according to the temperature of the engine coolant and engine
speed in order to compensate, during the warm up stage, for the increase in the ignition delay due to the
"low" temperatures in the combustion chambers.
Injection pressure check
This check is particularly important because the injection pressure affects the following parameters:
the quantity of fuel introduced into the cylinders in relation to the duration of the injection;
the atomization of the fuel injected;
the penetration of the jet;
the delay betweenthe electrical operation of the injector and the effective start and end of the injection.
The above mentioned parameters have a considerable influence on the behaviour of the engine, especially
as far as the power supplied, exhaust emissions, noise and driveability are concerned.
According to the engine load, the injection control unit operates the pressure regulator to always achieve
an optimum line pressure.
With the engine cold, the injection pressure is corrected according to the engine speed and the tempera-
ture of the engine coolant in order to satisfy the engine requirements at different operating temperatures.
Check on auxiliary electric fuel pump
The auxiliary electric fuel pump, immersed in the tank, is supplied by the injection control unit by means
of a relay when the ignition key is in the ON position.
The supply to the electric pump is inhibited when one of the following conditions is verified:
-after the ignition has been switched ON for a certain time and the engine is not started up;
-if the inertia switch has been operated.
Check on injection during deceleration (cut-off)
The fuel cut-off strategy is implemented when the injection control unit receives the information from the
potentiometer that the accelerator pedal is released.
Under these circumstances the control unit cuts off the supply to the injectors and reactivates before the
idle speed is reached.
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