Fiat 1998 Marea Service Manual page 297

Marea- Marea Weekend
99 update
0,995
mV
1000 H
8 0 0
600
4 0 0
200 H
0
0,7 0,8 0,9
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
Copyright Fiat Auto
ft
16v
X1.005
t
1,0 1,1 1,2 1,3
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.
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
Engine
Fuel system
10.
27