1989 Volvo 740
pg. 106 Servicing
Evaporative control system
The 740 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 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 fuel-induction system.
Crankcase ventilation
The engine is equipped 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 PCV nipple in the intake manifold should be removed and cleaned after 60,000 miles (96,000 km).
Check/replace hoses at the same time.
Exhaust Gas Recirculation (EGR)
This system operates by returning some of the exhaust gases to the engine to be recombusted: since this lowers the combustion temperature
the amount of nitrogen oxides released into the atmosphere is reduced.
The EGR valve should be inspected every 12,000 miles (20,000 km) and cleaned even 24,000 miles (40,000 km).
pg. 107 Servicing
WARNING!
The ignition system operates at very high voltages. Special safety precautions must be followed to prevent injury. Always turn the
ignition off when:
●
Connecting engine test and diagnostic equipment to the vehicle (timing light, tach-dwell tester, ignition oscilloscope, etc).
●
Replacing ignition components e.g. plugs, coil. distributor, HT leads etc.
●
Do not touch any part of the ignition system while the engine is running. This may result in unintended movements and body injury.
Replacing spark plugs
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