Checking The Gap; Detonation Sensors - Fiat 1998 Marea Service Manual

Engine
Fuel system
When measuring the distance it is im-
perative to be at right angles with the
flywheel and corresponding to a tooth
and not a gap.
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Checking the gap

The rpm and TDC sensor is fixed directly to
the cylinder block/crankcase and therefore the
gap and the angular position no longer need
to be adjusted. If a fault is suspected it is,
however, possible to check the gap, proceed-
ing as follows:
- remove the rpm and TDC sensor;
- check that the distance between the surface
of the sensor and the flywheel tooth corre-
sponds to the sum of the length of the sen-
sor (34.5 mm) and the gap (0.8 - 1.5 mm).

DETONATION SENSORS

(0.261.231.131)
The detonation sensors are located on the
monobloc under the inlet manifolds and be-
tween cylinders 1 -2 and 4-5.
These sensors have a bush to prevent incor-
rect torque tightening.
In the case of replacement, do not place
washers or shims between the cylinder
block/crankcase and sensor contact sur-
faces.
When the engine is knocking (detonation),
vibrations of a certain frequency are produced
in the cylinder block/crankcase.
This phenomenon produces a mechanical re-
percussion on a piezoelectric crystal which
sends a signal to the control unit; on the basis
of this signal the control unit reduces the ig-
nition advance (from 3° up to a maximum of
9.7°) until the phenomenon disappears. Later
on, the advance is gradually restored to the
basic value.
Connector wiring
The sensors are connected to the electronic
control unit (Pins M22/M54 and M38/M6)
by means of twisted cables with a protective
outer casing.
The numbers indicate the corresponding con-
trol unit pins.
99 range
Print n° 506.763114