Firebird V8-350 5.7L VIN P SFI (1996)
![background image](/pontiac/firebird/v8-350_5.7l_vin_p_sfi/Page-1112001.png)
Positive Crankcase Ventilation Valve: Description and Operation
PCV Valve
DESCRIPTION
The Positive Crankcase Ventilation (PCV) valve, consists of a needle valve, spring and housing.
OPERATION
Engine Off
When the engine is off, the spring holds the needle valve closed to stop vapors from entering the intake manifold.
Engine Running
When the engine is running, manifold vacuum lifts the valve off its seat and allows crankcase vapors to enter the intake manifold.
Idle Quality Control
To maintain idle quality, the PCV valve restricts the flow when the intake manifold vacuum is high.
Engine Backfire
In case of an engine backfire, in the intake manifold, the valve closes. This stops the backflow of gases and prevents the ignition of fuel vapor in the
crankcase.
EXCESSIVE BLOW-BY
During certain engine conditions, more blow-by gases are produced than the PCV valve can handle. In this case, the excess gases are returned
through the air intake tube to the air cleaner or intake manifold, where they are burned in the combustion chamber.