DESCRIPTION
Gasoline models use a closed crankcase ventilation system. The system consists of a hose connecting the air cleaner and valve cover and a hose connecting the crankcase or valve cover to the intake manifold. The intake manifold hose has a ventilation valve or calibrated orifice in it. Hose connections vary with engine models, as shown in illustrations.
SYSTEM OPERATION
Air enters system from air cleaner through hose to valve cover. Fresh air mixes with crankcase fumes and enters ventilation tube into valve or orifice. The valve or orifice regulates ventilation flow. The air is then drawn into the intake manifold where it is burned.
PCV VALVE
Valve is operated by pressure difference between crankcase and intake manifold. When there is no pressure difference (engine not running) or when pressure of intake manifold is greater than that of crankcase, valve is closed.
During engine idle, high manifold vacuum overcomes valve spring and valve is pulled toward intake manifold side by vacuum. This causes air to pass through restricted passage between valve and housing. During normal engine operation, valve stays in a position where spring pressure and intake manifold vacuum balance. Amount of air flow then depends on position of valve.
MAINTENANCE
After long periods of engine operation, ventilation valve tends to become clogged, which will affect proper engine operation. Every 30,000 miles for Federal vehicles or 60,000 miles for California vehicles, clean and inspect system and replace PCV valve.
Crankcase Ventilation System (Pickup & 4-Runner - Carburetor Models). Scheme 6
Crankcase Ventilation System (Land Cruiser). Scheme 7
Crankcase Ventilation System (Cressida & Supra). Scheme 8
Crankcase Ventilation System (Celica, Pickup & 4-Runner - Fuel Injection Models). Scheme 9
Crankcase Ventilation System (Tercel & Corolla). Scheme 10
Crankcase Ventilation System (Camry). Scheme 11
Crankcase Ventilation System (Van). Scheme 12
Crankcase Ventilation System (MR2). Scheme 13
Remove PCV valve and attach a clean piece of hose to cylinder head end of valve. Blow through valve with mouth pressure; air should pass through. Move clean hose to intake manifold end of valve and again blow through valve; air should pass through with difficulty. Replace valve if defective.
