Emission Control System - Porsche 928 1980 Owner's Manual

How Emission Control Works
When an automobile engine is running, it
uses energy generated through the com-
bustion of a mixture of air and fuel. Depend-
ing on whether a car is driven fast or slow
or whether the engine is cold or hot, some
of the fuel (hydrocarbons) may not be burn-
ed completely but be discharged into the
engine crankcase or exhaust system. Addi-
tional hydrocarbons may enter the atmo-
sphere through evaporation of fuel from the
fuel tank. These hydrocarbons (HC), when
released into the air, contribute to undesir-
able pollution.
In addition, carbon monoxide (CO) and
oxides of nitrogen (NO ) contribute to harm-
x
ful engine emissions. They, too, are formed
during the combustion process and dis-
charged into the exhaust system. To reduce
these pollutants to a minimum, your Porsche
is equipped with a Lambda Emission
Control System.
Controlled Combustion System
The amount of pollutants emitted from an
engine greatly depends on the combustion
of the air/fuel mixture. Complete burning of
the air/fuel mixture is therefore very impor-
tant. An improved combustion process in
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 (OXS)
The oxygen sensor installed in the exhaust
manifold makes it possible to maintain the
air/fuel mixture ratio at the desired lever of
lambda = 1.0. The oxygen sensor continu-
ously measures the oxygen content of the
exhaust gas and signals the information to
an electronic control unit. The control unit
corrects the air/fuel ratio, so that the engine
always receives an accurately metered air
fuel mixture. The lambda control system is
monitored by the oxygen sensor (see
"Warning lights").
Three way catalytic converter
Harmful pollutants in the exhaust gas can be
reduced to a minimum with the three way
catalytic converter. However, the catalytic
converter can only achieve this reduction
with the aid of the lambda control system.
This system is designed to maintain close
control of the air/fuel mixture ratio under all
operating conditions. At an air/fuel mixture
ratio of 14.5 to 1 (lambda = 1.0), hydro-
carbons (HC), carbon monoxide (CO) and
oxides of nitrogen (NO ) can be controlled
x
efficiently and simultaneously by the three
way catalytic converter. If, at any time, the
air/fuel mixture ratio is either below or in
excess of lambda = 1.0, pollutants increase.
The use of UNLEADED FUEL is critically
important. Deposits from leaded gasolines
will make the catalytic converter ineffective
as an emission clean-up device. Therefore
only unleaded gasoline without harmful
additives must be used.
Crankcase Ventilation
Through Crankcase Ventilation harmful
emissions from the engine crankcase are
not permitted to reach the outside atmo-
sphere. 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.
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