Fiat 1998 Marea Weekend, Service Manual

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Engine
Fuel system
Marea- Marea Weekend ©
99 range
1. Deflector (pulley seal)
2. Magnetic material
TIMING SENSOR (0.232.101.026)
The injection system in the Bosch Motronic ME
3.1 system is the phased, sequential type, i.e. the
injection of the fuel takes place in sequence for
each cylinder during the inlet stroke.
To achieve this, in addition to the rpm and TDC
signal, the electronic control unit also uses a tim-
ing signal to determine the point of injection.
The signal sent to the control unit is produced by
a Hall effect sensor fitted by the exhaut side cam-
shaft drive pulley.
Operating principle
A semi-conductor layer through which a current passes, immersed
in a normal magnetic field (lines of force perpendicular to the di-
rection of the current), produces a difference in power at its ter-
minals known as HALL voltage.
If the intensity of the current remains constant, then the voltage
produced only depends on the intensity of the magnetic field; the
intensity of the magnetic field simply has to be periodically altered
to produce a modulated electrical signal whose frequency is pro-
portional to the speed at which the magnetic field changes.
To produce this change, a metal ring (inner part of the pulley)
with an opening is passed through the sensor. As it moves, the
metal part of the ring covers the sensor, stopping the magnetic
field with a consequent low output signal; conversely, for the
opening, where the magnetic field is present, the sensor produces
a high signal.
As a result, a high signal alternates with a low signal once for every two revolutions of the engine, namely
when cylinder N°1 is 78° before TDC. This signal, together with the rpm and TDC signal, allows the control
unit to recognize the cylinders and determine the point of injection. For each engine revolution the control
unit checks that there is a timing signal; if this signal is missing for two consecutive revolutions, the control
unit signals the fault (warning light in the dashboard comes on) and does not allow the engine to be started
up.
Connector wiring
The numbers indicate the corresponding con-
trol unit pins
Removing-refitting
This operation involves the removal of the toothed
belt from the timing system and from the exhaust
side camshaft toothed pulley.
Having carried out these operations, it is neces-
sary to:
- disconnect the electrical connector;
- undo the fixing bolts and remove the sensor.
When refitting, reverse the order of the operations
carried out for the removal, following the instruc-
tions for refitting and tensioning the toothed belt.
NOTE 777e sensor does not require any type of
adjustment
22
Print n° 506.763/14