DESCRIPTION
The positive crankcase ventilation system is used to provide for more effective elimination of crankcase vapors. Fresh air from the air filter housing is supplied to the crankcase where it is mixed with blow-by gases and passed through a Positive Crankcase Ventilation (PCV) valve into the intake manifold. This mixture is then passed into the combustion chamber and burned.
OPERATION
The PCV valve provides primary control in this system by metering the flow of the blow-by vapors, according to manifold vacuum. When manifold vacuum is high (at idle) the PCV restricts the flow to maintain a smooth idle condition.
Under conditions where abnormal amounts of blow-by gases are produced (such as worn cylinders or rings), the system is designed to allow the excess gases to flow back through crankcase vent hose into the air inlet and be consumed during normal combustion. (Scheme 18)
Scheme 18
REQUIRED SERVICE
The PCV system may require service for obstructions if any of the following conditions exist
- Rough Idle.
- Stalling or slow idle speed.
- Oil leaks.
- Oil in air cleaner.
- Sludge in engine.
A leaking valve or hose could cause
- Rough Idle.
- Stalling.
- High idle speed.
If an engine is idling rough, check for clogged PCV valve, plugged or broken hoses BEFORE adjusting idle. Check part No. of PCV valve to ensure the correct valve is fitted. Replace PCV valve if required.
CHECKING PCV VALVE FUNCTION
- Remove PCV valve from rocker cover. Run engine at idle. Place thumb over open end of PCV valve to check for vacuum. If there is no vacuum at valve, check for obstruction in manifold port, hoses or PCV valve. Repair or replace as necessary.
- Turn engine off. Remove PCV valve. Shake valve and listen for rattle of check valve inside. If a clear rattle is not heard, replace PCV valve.
- Visually inspect valve for varnish or deposits which may make PCV valve operation sticky, restricted or cause incomplete seating of valve. Replace if necessary. An engine must be sealed for the PCV system to function as designed. If leakage, sludging or dilution of oil is noted AND the PCV system is functioning properly, check engine for cause and repair as required to insure PCV system will continue to function properly. An engine operating without any crankcase ventilation can be damaged so it is important to replace PCV valve and air cleaner breather at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.
SYSTEM TESTING
Note. Testing information not available.