Fiat 1998 Marea Weekend, Service Manual

Page: 355 / 846

Engine
Fuel system
Marea- Marea Weekend ft
99 range
10.
6 7
4A30U01
1. Connecting cable
2. Protective sleeve
3. Planar sensor element
4. Ceramic support pipe
5. Sensor housing
6. Ceramic seal
7. Protective tube
LAMBDA SENSOR (B.258.040.092)
The Lambda sensor is the "planar" type, fitted
on the front section of the exhaust pipe and
informs the injection control unit of the prog-
ress of the combustion (stoichiometric ratio).
To obtain an ideal mixture the quantity of air
drawn in by the engine must be equal to the
theoretical amount required to burn all the fuel
injected.
In this case the Lambda factor
(X)
i.e. the ratio
between the quantity of intake air and the
theoretical quantity of air (which is required to
burn all the fuel injected) is equal to 1.
Therefore:
X =
1 ideal mixture
X >
1 lean mixture
X <
1 rich mixture
4A30UI02
a. Rich mixture (lack of air)
b. Lean mixture (excess air)
The Lambda sensor, in contact with the ex-
haust gases, produces an electrical signal,
whose voltage value depends on the concen-
tration of oxygen in the actual gases.
This voltage undergoes a sharp variation when
the composition of the mixture shifts from the
value
X
= 1.
The heating of the Lambda sensor is managed
by the injection control unit proportionally to
the temperature of the exhaust gases.
This prevents thermal shocks to the ceramic
casing due to contact with the condensed
water present in the exhaust gases when the
engine is cold.
The measuring cell and the heater are incor-
porated in the "planar" stratified ceramic ele-
ment with the advantage of the rapid heating
of the cell to allow the closed loop control
(=1) within several seconds of the engine be-
ing started up.
Connector wiring
The numbers indict the corresponding control
unit pins.
3 0
Print n° 506.763/14