Porsche 911 Carrera - Manual (Page 250)

How Emission Control Works
When an automobile engine is running, it uses
energy generated through the combustion of a
mixture of air and fuel. Depending on whether a car
is driven fast or slowly or whether the engine is cold
or hot, some of the fuel (hydrocarbons) may not be
burned completely, but may be discharged into the
engine crankcase or exhaust system. Additional
hydrocarbons may enter the atmosphere through
evaporation of fuel from the fuel tank. These
hydrocarbons (HC), when released into the air,
contribute to undesirable pollution.
In addition, carbon monoxide (CO) and oxides of
nitrogen (NOx) contribute to engine emissions.
They, too, are formed during the combustion
process and discharged into the exhaust system.
To reduce these pollutants, your Porsche is
equipped with a precisely calibrated fuel injection
system to assure a finely balanced air/fuel mixture
under all operating conditions.
Oxygen sensor
The oxygen sensor, installed in the exhaust
pipe continuously senses the oxygen content
of the exhaust and signals the information to an
electronic control unit. The control unit corrects
the air/fuel ratio, so the engine always receives an
accurately metered air/fuel mixture.
Crankcase ventilation
Through crankcase ventilation, undesirable
emissions from the engine crankcase are not
permitted to reach the outside atmosphere. These
emissions are recirculated from the crankcase to
the air intake system. From here the emissions
mix with the intake air and are later burned in the
engine.
Catalytic converters
The catalytic converters are efficient “clean-up”
devices built into the exhaust system of the vehicle.
The catalytic converters burn the undesirable
pollutants in the exhaust gas before it is released
into the atmosphere.
The exclusive use of unleaded fuel is critically
important for the life of the catalytic convert-
ers. Therefore, only unleaded fuel must be
used.
The catalytic converters will be damaged by:
– push or tow starting the vehicle
– misfiring of the engine
– turning off the ignition while the vehicle is
moving or
– driving until the fuel tank is completely empty
– by other unusual operating conditions.
Do not continue to operate your vehicle under
these conditions, since raw fuel might reach
the catalytic converters. This could result in
overheating of the converters. Federal law
prohibits use of leaded fuel in this car.
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Maintenance, Car Care