Crankcase Ventilation System Inspection/Diagnosis

Crankcase Ventilation System Inspection/Diagnosis





If an engine is idling rough, check for a clogged PCV valve. Replace if required. Use the following procedure:

1. Check the PCV valve (1), hoses (2), and connections for leaks or restrictions.
2. At idle, listen to the PCV valve (1) with a stethoscope as you lightly pinch the PCV hose (2) with your fingers or pliers for several times. Each time the hose is pinched, the valve should click.
3. If there is no clicking should, check the PCV valve grommet for cracks or damage. If the grommet is OK, replace the PCV valve and recheck.
With this system, any blow-by in excess of the system capacity is exhausted into the intake manifold and is drawn into the engine. Proper operation of the crankcase ventilation system is dependent upon a sealed engine. If oil sludging or dilution is noted, and the crankcase ventilation system is functioning properly, check engine for possible cause and correct to ensure that the system will function as intended.

Crankcase Ventilation System Description
A crankcase ventilation system is used to consume crankcase vapors in the combustion process instead of venting them to the atmosphere. Fresh air from the throttle body is supplied to the crankcase, mixed with blow-by gases, then passed through the PCV valve into the intake manifold.

Operation
The primary control is through the Positive Crankcase Ventilation (PCV) valve which meters the flow at a rate depending on the inlet vacuum. To maintain idle quality, the PCV valve restricts the flow when the inlet vacuum is high. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase vent into the throttle body to be consumed by normal combustion.

Results of Incorrect Operation
A plugged valve may cause the following conditions:
^ Rough idle
^ Stalling or slow idle speed
^ Oil deterioration A leaking valve would cause
^ Rough idle
^ Stalling
^ High idle speed