A crankcase ventilation system is used to consume crankcase vapors in the combustion
process instead of venting them to atmosphere. Fresh air from the throttle body is supplied to
the crankcase, mixed with blow by gases and then passed through a PCV valve into the intake

The primary control is through the positive crankcase ventilation (PCV) valve which meters the
flow at a rate depending on inlet vacuum. To maintain idle quality, the PCV valve restricts the
flow when inlet vacuum is high. If abnormal operating conditions arise, the system is designed to
allow excessive amounts of blow by gases to back flow through the crankcase vent into the
throttle body to be consumed by normal combustion.

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PCV Valve Operation And Description