Fiat 1998 Marea Weekend, Service Manual

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Marea- Marea Weekend ft
99 update
16v
Engine
Fuel system
mV
1000 H
8 0 0
6 0 0
4 0 0
200 H
0
0,995
X 1 . 0 0 5
t
0,7 0,8 0,9 1,0 1,1 1,2 1,3
10.
LAMBDA SENSOR
The Lambda sensor measures the oxygen con-
tent in the exhaust gases: it is fitted on the ex-
haust pipe, upstream of the catalytic silencer.
The sensor output signal is sent to the control
unit for feed-back correction of the mixture
strength.
When the sensor provides a low signal (volt-
age below 200 mV) the control unit recognizes
a poor mixture and increases the injection time;
later on, when the sensor signal is high (volt-
age above 800 mV), the control unit recog-
nizes a rich mixture and decreases the injection
time.
This sequence is repeated at a frequency in the
order of tens of Hertz so that the engine runs
with a mixture strength continuously fluctuat-
ing around the stoichiometric level.
At temperatures below 300°C the ceramic ma-
terial is not activated, therefore the sensor does
not send reliable signals: to make sure that it
heats up quickly during starting and the tem-
perature is maintained whilst idling, the sensor
is fitted with a heater with an electrical resis-
tance which is always on.
The sensor can be rapidly put out of
action by the presence of even slight
amounts of lead in the fuel.
X
= 1 Ideal mixture (stoichiometric)
X >
1 Lean mixture
Excess air, the CO values tend to be low
X<
1 Rich mixture
Lack of air; the CO values tend to be high
Wiring connector
The sensor heating resistance can be measured
by disconnecting the connector and connector
an ohmmeter as illustrated in the diagram.
Resistance: 4.5 ± 0.5 ohm at 20°C
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