The PCV system operates by engine intake manifold vacuum. Filtered air is routed into the crankcase through the air cleaner hose and crankcase breather(s) (if used). 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.

TYPICAL PCV valves are shown.

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.

Fig 1: Identifying Engine Off Or Engine Pop-Back-No Vapor Flow

Courtesy of DAIMLERCHRYSLER CORP.

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.

Fig 2: Identifying High Intake Manifold Vacuum-Minimal Vapor Flow

Courtesy of DAIMLERCHRYSLER CORP.

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 3: Identifying Moderate Intake Manifold Vacuum-Maximum Vapor Flow

Courtesy of DAIMLERCHRYSLER CORP.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

PCV Valve: Operation

Use the Manual With the Right Hardware

When to See a Mechanic