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1997 Volvo 850
This system adds air to the hot exhaust gases as they are expelled from the engine. This causes a
secondary combustion of residual hydrocarbons and carbon monoxide, resulting in lower emissions
levels in the exhaust gases.
Evaporative control system
The car is equipped with a gas evaporative control system, which prevents gasoline fumes from being
released into the atmosphere. The system is comprised of an expansion chamber in the fuel tank, a roll-
over valve on the cross member in front of the fuel tank and a charcoal canister with a built-in vacuum
valve under the left-front wheel housing. The components are interconnected by hoses which channel
fuel vapor from the gas tank to the charcoal filter, where it is stored until the engine is started and then
drawn into the engine's air intake system.
Crankcase ventilation
The engine is provided with positive crankcase ventilation which prevents crankcase gases from being
released into the atmosphere. Instead, the crankcase gases are admitted to the intake manifold and
cylinders.
PCV system
The orifice nipple in the intake manifold and the filter at the end of the PCV hose in the air cleaner
should be inspected every 60,000 miles (96,000 km). Check/replace rubber hoses at the same time.
file:///K|/ownersdocs/1997/1997_850/97850_806.htm (5 of 10)12/30/2006 10:14:29 AM