DESCRIPTION
Positive crankcase ventilation system is designed to prevent contaminating hydrocarbons, created in crankcase, from escaping into atmosphere.
Vapors are routed from crankcase through a vacuum controlled ventilating valve (PCV) into intake manifold. When vapors reach intake manifold, they are mixed with air/fuel mixture and burned in combustion process.
OPERATION
With engine operating, fresh air enters positive crankcase ventilation system through air cleaner assembly. Fresh air flows through crankcase breather and into rocker arm/valve compartment.
Entering fresh air combines with blow-by gases and unburned air/fuel mixture of crankcase. Combined gases are drawn into carburetor, through PCV valve, by manifold vacuum. Crankcase gases mix with air/fuel mixture and are burned in combustion chamber. (Scheme 34)
Positive Crankcase Ventilation System (Typical). Scheme 34
PCV valve is held closed by spring pressure when engine is not running. This prevents hydrocarbon fumes from collecting in intake manifold, resulting in hard starting. (Scheme 35)
Cutaway View of a Typical PCV Valve. Scheme 35
When engine is running, manifold vacuum pulls PCV valve open allowing crankcase fumes to enter intake manifold. A baffle in rocker arm cover prevents engine oil from being drawn into intake manifold.
If engine backfires through intake manifold, PCV valve closes and prevents any flow of gases through it. This is to prevent ignition of fumes in crankcase.
TESTING
Note. Testing information not available.
MAINTENANCE
An engine may idle slow or rough due to a clogged PCV valve or system. Never adjust idle speeds without first checking entire PCV system.
| CAUTION | If a PCV system component becomes clogged, all crankcase ventilation will stop and serious engine damage could occur. |
Although following manufacturer's service procedures is recommended, PCV system should be serviced more frequently if vehicle is operated under severe conditions (extreme dust, prolonged idling, trailer hauling or short trips in cold weather).
PCV VALVE
If PCV valve is clogged or defective, replace valve. DO NOT attempt to clean valve. Replace PCV valve every 30,000 miles on front wheel drive vehicles or every 52,500 miles on rear wheel drive vehicles.
FILTER ELEMENT
Replace filter element every 30,000 miles on front wheel drive vehicles or every 52,500 miles on rear wheel drive vehicles. Periodic cleaning of filter between replacement intervals may be required if vehicle is operated under severe operating conditions.