Fiat 1996 Brava Service Manual page 275

Engine
Fuel system
10.
1
mV
1000-
8 0 0 -
600-
4 0 0 -
200-
0 -
0 , 9 9 5 * • "
1
1
^ \ l , U U O
l
f
l l l i i i i »■
0,7 0,8 0,9 1,0 1,1 1,2 1,3
X=1 Ideal mixture (stoichiometric)
A. 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
Bravo-Brava )§i lev
98 range
LAMBDA SENSOR
The Lambda sensor measures the oxygen
content in the exhaust gases: it is fitted on the
exhaust pipe upstream of the catalytic si­
lencer.
The sensor output signal is sent to the control
unit for fee-back correction of the mixture
strength.
When the sensor provides a low signal (volt­
age below 200 mV), the control unit recog­
nizes a lean mixture and increases the injec­
tion time; later, when the sensor signal is high
(voltage above 800 mV), the control unit rec­
ognizes a rich mixture and decreases the in­
jection time.
This sequence is repeated at a frequency in
order of tens of Hertz so that the engine con­
stantly operates with a mixture strength close
to the stoichiometric ratio.
For temperatures below 300 °C, the ceramic
material is not activated, therefore the sensor
does not send plausible signals: to ensure
rapid heating during starting and maintain
the temperature during idling, the sensor is
fitted with a heater with the electrical resis­
tance always switched on.
The sensor can rapidly be put out of
action by the presence of even slight
amounts of lead in the fuel.
The sensor heater resistance can be mea­
sured by disconnecting the connector and
connecting an ohmmeter as shown in the di­
agram.
Resistance: 4.5+0.5 ohm at 20 °C
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Print no. 506.670/16