Fiat 1998 Marea Weekend, Service Manual

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Engine
Marea-Marea Weekend
@ t
Fuel system 1998
range
10.
When cold
Under these conditions, the mixture becomes naturally leaner due to reduced evaporation and heavy fu-
el condensation on the intake manifold internal walls. The greater viscosity of the lubrication oil also
brings about an increase in the rolling resistance of internal engine components which also serves to ex-
acerbate matters.
The electronic control unit recognises this condition and corrects injection time on the basis of the
coolant temperature signal.
P4F06IJ01
Consequently:
- At very low temperatures the injector stays open longer Tj) graph (b) for a low air fuel ratio (rich mix-
tures);
- As engine temperature increases, injector opening time becomes shorter (tj) graph (a) and the air/fuel
ratio becomes correspondingly higher (lean mixture).
While the engine is warming up, the ECU also governs a step motor which is responsible for calculating
the amount of air necessary to ensure the engine does not stall.
Rpm is decreased as the temperature rises until the rated level is reached (850 ± 30 Rpm) when the en-
gine is warm. The ECU governs the step motor to maintain idle speed constant even if electrical and me-
chanical loads vary.
Connection to automatic transmission
The ECU adjusts engine idle speed on the basis of the load input when the selector lever is moved to a
given position and transmits information to the automatic transmission ECU on torque reduction (pin
36), engine coolant temperature (pin 5) and throttle valve position (pin 16).
The control unit reduces the level of torque produced by the engine (mainly by altering ignition ad-
vance) during gear changes, when it receives a signal from the automatic transmission control unit (pin
49).
Full-load
Under full load conditions, base pulse constant must be increased to obtain maximum engine power
output.
The ECU detects a full load condition as a result of parameters supplied by the throttle position and ab-
solute pressure sensors.
On the basis of this information, the ECU implements the appropriate correction strategy by increasing
base pulse constant.
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Publication no. 506.763/09