For 1990-2009 cars

(1) | Breather Hose
(2) | Intake Manifold
(3) | Fresh Air
(4) | Blowby Gas
(5) | PCV Valve
(6) | Valve Cover

The compressed combustion gas which escapes past the piston rings into the crankcase is known as blow-by gas. Blow-by gas contains large amounts of CO and HC. The positive crankcase ventilation (PCV)system prevents the blow-by gas from being emitted into the atmosphere. The PCV system routes the crankcase blow-by gas back into the intake system where the blow-by gas becomes part of the combustion process. The PCV system consists of the following components:

• | The PCV valve

• | The crankcase vent (breather) or air inlet tube

• | The air inlet filter or separator, if used

• | Any hoses or couplers

### Operation

The primary control of engine crankcase blow-by gas is the PCV valve. The PCV valve meters the flow of blow-by gas according to the manifold vacuum signal.

#### PCV Valve

In order to maintain idle quality, the PCV valve restricts the flow of blow-by gas whenever the intake manifold vacuum is high. Abnormally high crankcase pressure may cause the blow-by gases to flow through the crankcase vent tube and into the air cleaner. The blow-by gases are then drawn into the intake system and consumed in the normal combustion process. The relationship between the flow of blow-by gas and the engine manifold vacuum is charted in the following table:

#### PCV Valve Operation

Manifold Vacuum | PCV Valve Opening | Blow-by Gas Flow
--- | --- | ---
Low | Large | High
High | Small | Low

### Results Of Incorrect Operation

A plugged valve or hose may cause any of the following conditions:

• | A rough engine idle

• | Engine stalling or low engine idle speed

• | High engine crankcase pressure

• | Engine oil leaks

• | Engine oil in the air cleaner

• | Oil sludge in the engine

• | Engine oil consumption

• | Excessive exhaust emissions

A leaking valve or hose may cause any of the following conditions:

• | A rough engine idle

• | Engine stalling

• | High engine idle speed

• | Incorrect engine crankcase pressure

• | Excessive exhaust emissions