Porsche carrera gt-2004 Manuel D’Utilisation

Maintenance, Car Care

129

How Emission Control Works 

When an automobile engine is running, it uses en-

ergy generated through the combustion of a mix-

ture 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. Additon-

al 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 pro-

cess 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 

Oxygen sensors, installed in the exhaust pipe con-

tinuously senses the oxygen content of the 

exhaust and signals the information to an electron-

ic control unit. The control unit corrects the air/

fuel ratio, so the engine always receives an accu-

rately metered air/fuel mixture. 

Crankcase ventilation 

Through crankcase ventilation, undesirable emis-

sions from the engine crankcase are not permit-

ted to reach the outside atmosphere. These emis-

sions 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 en-

gine. 

Catalytic converters 

The catalytic converters are efficient “clean-up” 

devices built into the exhaust system of the vehi-

cle. The catalytic converters burn the undesirable 

pollutants in the exhaust gas before it is released 

into the atmosphere. 

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 mov-

ing or 

– driving until the fuel tank is completely empty 
– by other unusual operating conditions. 
f 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 pro-

hibits use of leaded fuel in this car.