Fiat Bravo Service Manual page 237

Bravo-Brava ty
16v
Engine
Fuel system
10.
mV
1000
8 0 0
6 0 0
4 0 0
2 0 0 - |
0
0,995
\
* X 1,005
t
— i r-
0,7 0,8 0,9 1,0 1,1 1,2 1,3
T *■
P4A27BJ02
lambda = 1: stoichiometric mixture
lambda < 1 : rich mixture, the CO values tend to be high
lambda > 1 : lean mixture, the CO values tend to be low
Wiring connector
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 to correct (feed-back) the mixture stren­
gth.
When the sensor supplies a low signal (volt­
age below 200 mV) the control unit recog­
nizes a lean mixture and increases the injec­
tion time; subsequently, when the sensor sig­
nal is high (voltage above 800 mV), the con­
trol unit recognizes a rich mixture and de­
creases the injection time.
This sequence of operations is repeated with
a frequency in the order of tens of Hertz, so
that the engine operates with a mixture stren­
gth constantly oscillating around the stoi­
chiometric value.
At temperatures below 300°C the ceramic
material is not activated, therefore the sensor
does not send reliable signals: to ensure rapid
heating during starting and to maintain the
temperature during idling, the sensor is
equipped with a heater where the electrical
resistance is always on.
The sensor can be rapidly put out of
action by the presence of even the
smallest amounts of lead in the fuel.
The resistance of the sensor heater can be
measured by disconnecting the connector
and connecting an ohmmeter as shown in
the diagram.
Resistance: 4,5 ± 0,5 ohm at 20°C
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