Knock Sensor (Kne-03) - Fiat Bravo Service Manual

Bravo- Brava 9
1998 range
1 2 3
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Copyright Fiat Auto
A A A
V
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K N O C K S E N S O R
(KNE-03)
This sensor is the piezoelectric type and is f i t -
ted on the cylinder block/crankcase in a p o s i -
tion w h i c h is symmetrical in relation t o the
pairs of cylinders 1 -2 and 3-4.
This position is determined by the need t o
detect the onset of knock in the same w a y for
all cylinders.
W h e n there is engine knock, vibrations of a
particular frequency are produced .
The effect generates mechanical repercussions
o n a piezoelectric crystal that sends a signal t o
a control unit. The control unit then reduces
the ignition advance on the basis of this signal
until the effect disappears. The advance
then gradually restored to the baseline value.
Principle of operation
The molecules in a quartz crystal are electri-
cally polarised.
Under rest conditions ( A ) , the molecules are
not aligned in any particular direction.
W h e n the crystal is subject t o pressure or i m -
pact ( B ) , the molecules line up and the degree
t o w h i c h they align is directly proportional t o
the pressure o n the crystal. This
creates a voltage at the crystal terminals.
A. Rest position
B. Position under pressure
Checking the resistance
The sensor resistance can be measured by dis-
c o n n e c t i n g the connector and c o n n e c t i n g an
ohmmeter t o the sensor terminals
Resistance 532 - 588 ohm at 20 C
Connector wiring
The sensor is connected t o the control unit by
t w i s t e d cables covered in a shielded
interference sheath.
Pin 1 - Earth
Pin 2 - Signal
Pin 3 - Shielding
The numbers in boxes
s p o n d i n g control unit pins.
Removing-refitting
Disconnect the electrical c o n n e c t i o n , u n d o the
knock sensor retaining bolt and remove.
Engine
Fuel system
10.
is
alignment
n o n -
indicate the corre-
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