Fiat 1998 Marea Weekend, Service Manual

Page: 171 / 846

Marea-Marea Weekend^
1998 range
16v
Engine
Fuel system
10.
8,9
mm
Q i
Qo
1 0 0
n° engine steps
-l 1—*
200 220
The electric step motor features extremely
high accuracy and resolution (about 220
steps per second). Pulses sent from the ECU
to the engine are converted from rotary mo-
tion into straight-line motion (about 0.04
mm/step) through a worm and screw mech-
anism. This operates a plunger which in turn
moves to alter the by-pass duct cross-sec-
tion.
The constant idle air flow Qo arises as a result
of leakage through the butterfly valve. This is
regulated during production and protected
by a cap. Maximum flow Q2 arises when the
plunger is fully retracted (about 200 steps
corresponding to 8.9 mm). Between these
two levels, air flow follows the graph shown
alongside.
Motor strategy
P 4 F 3 7 I J 0 1
The number of working steps is dependent upon engine conditions:
- Start-up stage
When the key is inserted, the ECU controls step motor position according to engine coolant tempera-
ture and battery voltage.
- Warming-up stage
Rpm levels are corrected according to engine coolant temperature.
- With engine warm:
Idle control is dependent on a signal from the rpm sensor. When external users are activated, the ECU
governs sustained idle.
- Over-run:
The ECU recognises over-run status from the throttle potentiometer position.
It controls step motor position by means of the idle flow law (DASH-POT laws). In other words, it slows
the return of pluger (3) to its seat so that a quantity of air by-passing hole (2) reaches the engine and re-
duces levels of pollutants in the exhaust gas.
Recovery
Actuator operation disenabled, self-adaption of idling fuel mixture level blocked and speed limited to 1200
rpm.
Removing-refitting engine idle control actuator (step motor)
- disconnect the battery negative terminal;
- unscrew both retaining screws and withdraw the actuator;
- check condition of thoroid seal and remove any impurities from the case seat;
- refit the actuator, checking that the plunger fits easily without forcing.
Tightening torque of step motor screws
0.35 - 0.45 da Nm.
Wiring connector
The numbers in boxes indicate the corre-
sponding control unit pins
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