Positive crankcase ventilation (pcv) system

DESCRIPTION

All 3.9L V-6 and 5.2/5.9L V-8 are equipped with a closed crankcase ventilation system and a positive crankcase ventilation (PCV) valve.

This system consists of a PCV valve mounted on the cylinder head (valve) cover with a hose extending from the valve to the intake manifold. Another hose connects the opposite cylinder head (valve) cover to the air cleaner housing to provide a source of clean air for the system. A separate crankcase breather/filter is not used.

OPERATION

The PCV system operates by engine intake manifold vacuum (Fig. 5). Filtered air is routed into the crankcase through the air cleaner hose. 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.

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 (Fig. 7). In this position there is minimal vapor flow through the valve.

Fig. 4 PCV Valve/Hose-Typical

1 - PCV VALVE

2 - PCV VALVE HOSE CONNECTIONS

Fig. 5 Typical Closed Crankcase Ventilation System

1 - THROTTLE BODY

2 - AIR CLEANER

3 - AIR INTAKE

4 - PCV VALVE

5 - COMBUSTION CHAMBER

6 - BLOW-BY GASES

7 - CRANKCASE BREATHER/FILTER

Fig. 6 Engine Off or Engine Pop-Back-No Vapor Flow

Fig. 7 High Intake Manifold Vacuum-Minimal Vapor Flow

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 (Fig. 8).

Fig. 8 Moderate Intake Manifold Vacuum-Maximum Vapor Flow