POSITIVE CRANKCASE VENTILATION VALVE
OPERATION
The PCV valve contains a spring loaded plunger.
The 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 backfire, the spring forces the plunger back
against the seat. This prevents vapors from flowing
through the valve (Fig. 6).
When the engine is at idle or cruising, high manifold
vacuum is present. At these times manifold vacuum is
able to completely compress the spring and pull the
plunger to the top of the valve (Fig. 7). In this position
there is minimal vapor flow through the valve.
During periods of moderate intake manifold vac-
uum the plunger is only pulled part way back from
the inlet. This results in maximum vapor flow
through the valve (Fig. 8).
Fig. 3 PCV Valve—2.4L Engine
1 – PCV VALVE
2 – INTAKE MANIFOLD
Fig. 4 PCV Valve —3.0L Engine
1 – PCV HOSE
2 – POSITIVE CRANKCASE VENTILATION (PCV) VALVE
3 – VALVE COVER
Fig. 5 PCV Valve and Fresh Air Hose— 3.3/3.8L
Engines
1 – THROTTLE BODY
2 – RESONATOR
3 – FRESH AIR HOSE
4 – PCV VALVE
Fig. 6 Engine Off or Engine Backfire—No Vapor
Flow
Fig. 7 High Intake Manifold Vacuum—Minimal Vapor
Flow
NS
EMISSION CONTROL SYSTEMS
25 - 25
DESCRIPTION AND OPERATION (Continued)
