Air Intake Circuit - Fiat 1998 Marea Service Manual

Engine
Fuel system
10.
Management of the climate control system
The injection/ignition control unit is functionally connected to the climate control system as follows:
1. it receives the request to engage the compressor from the climate control unit via pin F6 and operates
the various interventions (additional air);
2. it gives the go ahead to engage the compressor via pin F13 when the strategy conditions are verified;
3. it receives information on the four stage pressure switch status from pins F9 and F41 and operates the
interventions (operation of radiator fan).
As far as point 1 is concerned, if the engine is idling, the control unit increases the flow rate of the air
passing through the motorized butterfly casing before the compressor is switched on and, conversely, it
returns the actual to the normal position after the compressor is switched off.
As far as point 2, on the other hand, is concerned, the control unit automatically switches off the com-
pressor:
- for several seconds (timed disengagement):
- in high engine power requirement conditions (fierce acceleration);
- during engine take-off;
- as long as the following critical conditions persist:
- at engine coolant temperatures above a certain level;
- at engine speeds above or below a certain level.
Management of the radiator fan
The control unit directly controls the operation of the radiator fan according to the temperature of the en-
gine coolant and the engagement of the climate control system.
The fan comes on when the temperature exceeds 98°C (1st speed) and 101°C (2nd speed). It is switched
off with a hysteresis of 2°C below the temperature threshold.

AIR INTAKE CIRCUIT

The 1998 5 cylinder 20 valve version is equipped with a special air intake system. The manifold consists of
two half shells and an internal rocker element (module) which, operated by a special pneumatic actuator,
can assume two positions producing different inlet manifold lengths (variable geometry).
In this way it is possible to create five long (torque) ducts or five short (power) ducts.
The two different length ducts operate alternately allowing maximum volumetric efficiency at different
speeds.
By selecting the appropriate length inlet manifold it is possible to ensure that the fluctuations in the col-
umn of gas entering are phased with the movement of the valve to increaes the inertia effect of the gase-
ous mass in the cylinder.
This makes it possible to achieve a better degree of filling than usual.
Obviously, the device works within a hysteresis range, i.e. the shifts from the "power" manifold and
viceversa do not always take place at the same engine speed.
This is to avoid the possibility of balanced conditions being created and too rapid a succession of move-
ments from one length to another with obvious operating problems.
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Marea- Marea Weekend ©
99 range
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