Fiat 1996 Brava Service Manual page 328

Engine
Fuel system
10.
Bravo *£l 20v
98 range
1. Deflector (pulley ring)
2. Magnetic material
TIMING SENSOR (0.232.101.026)
In the Bosch Motronic ME 3.1 system the injec­
tion is the sequential, phased type, in other
words the fuel is injected in sequence for each
cylinder during the inlet stroke.
In order to achieve this, in addition to the rpm
and TDC signal, the electronic control unit also
uses a timing signal to determine the injection
point.
The signal sent to the control unit is produced
by a Hall effect sensor fitted by the camshaft
drive pulley, exhaust side.
Operating principle
P4A22LJ01
A semi-conductor layer, which the current passes through, im­
mersed in a normal magnetic field (lines of force perpendicular to
the direction of the current) produces a difference in power,
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 only needs to vary periodically in
order to produce a modulated electrical signal, whose frequency
is proportional to the speed at which the magnetic field changes.
To achieve this change, a metal ring (internal part of the pulley)
with an opening passes through tiie sensor. As it moves the met­
al part of the ring covers the sensor, blocking the magnetic field
with a consequent low output signal; conversely, when the
opening is present and consequently there is a magnetic field,
the sensor produces a high signal.
As a result the high signal alternates with the low signal once for every two revoluations 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 injection point. For each engine revolution, the control unit checks that the timing signal
is present; if this signal is missing for two consecutive revolutions, the control unit signals a fault (warn­
ing light in the instrument panel comes on) and the engine cannot be started up.
Wiring connector
The numbers indicate the corresponding con­
trol unit pins
I I
1 2
M51
3
M
M42
26
Removing- refitting
This operation involves the removal of the
toothed belt from the timing drive and the ex­
haust side camshaft pulley.
When these operations have been carried out:
- disconnect the electrical connector;
- undo the fixing bolts and remove the sensor.
When refitting, reverse the order of the opera­
tions, following the instructions for refitting and
tensioning the toothed belt.
NOTE The sensor does not require any type
of adjustment.
22
Print no. 506.670/16