Timing Sensor - Fiat 1998 Marea Service Manual

Engine
Fuel system
10.

TIMING SENSOR

This sensor is the Hall effect type and is fitted on the cylinder head facing the camshaft pulley (exhaust).
There is an opening in the pulley which allows the timing sensor to detect and signal the engine timing
position to the injection control unit.
The injection control unit uses the timing senor signal to recognize TDC at the end of the compression
stroke.
Operation
A semi-conductor layer, through which current flows, immersed 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, the voltage produced only depends on the intensity of the
magnetic field; the intensity of the magnetic field simply needs to vary periodically to produce a modulated
electrical signal whose frequency is proportional to the speed at which the magnetic field changes.
To obtain this change, the sensor passes through a metal ring (inner part of the pulley) with an opening.
As the metal part of the ring moves it covers the sensor blocking the magnetic field with a consequent low
output signal; conversely, corresponding to the opening and the presence of the magnetic field, the sensor
produces a high signal.
This signal, together with the rpm and TDC signals, allow the injection control unit to recognize the posi-
tion of the pistons and determine the injection point.
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Marea- Marea Weekend
AIR FLOW METER
The flow meter is on the air inlet hose and is the
heated film type.
The intake air temperature sensor is inside the flow
meter.
Operation
The operating principle is based on a heater dia-
phragm in a measuring duct through which the in-
take air entering the engine flows.
The hot film diaphragm is kept at a constant tem-
perature (about 120 °C above the temperature of
the intake air) by the heating resistance.
The mass of air passing through the measuring duct
tends to remove heat from the diaphragm therefore,
in order to keep the latter at a constant temperature,
a certain current must pass through the resistance.
This current, being proportional to the mass of air
flowing to the engine, is measured by a suitable
Wheatstone bridge and the signal is sent to the in-
jection control unit.
1. Covers
2. Electronic card
3. Sensor
4. Support plate
5. Support
6. Seal (O-Ring)
7. Temperature sensor
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