Positive Crankcase Ventilation: Description and Operation

PCV SYSTEM
This engine is equipped with a closed crankcase ventilation system and a Positive Crankcase Ventilation ([1][2]PCV) valve.

This system consists of:

Fig.2 PCV Valve/Oil Filler Tube (Housing):

- a PCV valve mounted to the oil filler housing. The PCV valve is sealed to the oil filler housing with an O-ring.
- the air cleaner housing

Fig.3 PCV System Hoses/Tubes:

- two interconnected breathers threaded into the rear of each cylinder head.
- tubes and hose to connect the system components.

The PCV system operates by engine intake manifold vacuum. Filtered air is routed into the crankcase through the air cleaner hose and crankcase breathers. The metered air, along with crankcase vapors, are drawn through the PCV valve and into a passage in the intake manifold. The PCV system manages crankcase pressure and meters blow-by gases to the intake system, reducing engine sludge formation.

The PCV valve contains a spring loaded plunger. This plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum.

Fig.4 Engine OFF Or Engine Pop Back - No Vapor Flow:

Fig.5 High Intake Manifold Vacuum - Maximum Vapor Flow:

Fig.6 Moderate Intake Manifold Vacuum - Maximum Vapor Flow:

TYPICAL PCV valves are shown in, and.

When the engine is not operating, or during an engine pop-back, the spring forces the plunger back against the seat. This will prevent vapors from flowing through the valve.

During periods of high manifold vacuum, such as idle or cruising speeds, vacuum is sufficient to completely compress spring. It will then pull the plunger to the top of the valve. In this position there is minimal vapor flow through the valve.

During periods of moderate manifold vacuum, the plunger is only pulled part way back from inlet. This results in maximum vapor flow through the valve.