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Fuel injection-ignition system components
The outer surface of the zirconium dioxide element is exposed to the exhaust gas, whereas the inside
is vented to the atmosphere. Both the inner and outer surfaces are coated with a thin layer of
platinum. Oxygen ions flowing through the ceramic electrically charge the platinum layer, which acts
as an electrode and produces a measurable voltage; this voltage is delivered to sensor output and on
to the connection cable attached to it.
The zirconium dioxide element becomes permeable to oxygen ions when heated up to about 300 °C.
The sensor uses the special physical properties of zirconium dioxide to generate a voltage relating to
the difference in oxygen content of the gases on either side of the element. A lean mixture produces a
low voltage signal, whereas a rich mixture will result in a high voltage output.
The sensor is set to change its output at an air/fuel ratio of 14.7:1 (14.7 parts of air to 1 part of fuel)
known as Lambda 1. This is considered as the ideal ratio for complete combustion, hence the name
Lambda Sensor: therefore
lambda = 1 means stoichiometric mixture ratio
lambda >1 means lean mixture
lambda <1 means rich mixture
The air/fuel mixture control system varies mixture content based on the information provided by the
sensor, which starts operating above 300°C: the ceramic core becomes permeable to oxygen ions
when heated up to about 300°C. Due to the particular characteristics of the material, the difference in
oxygen content on either side of the sensor generates a voltage across the two electrodes. And this
allows measuring the difference in oxygen content of exhaust gases and the environment. When the
air/fuel mixture sent to the combustion chamber is not correct, gases produced after engine
combustion still feature a residual oxygen content. This system then controls the fuel injection
electronic control unit so that engine always uses ideal mixture.
Unscrew the lambda sensor (1) from the exhaust pipe to remove it.
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