Mistascott
03-05-2004, 03:38 PM
The Positive Crankcase Ventilation (PCV) system is designed to eliminate vapors/gases that get past the pistons and into the crankcase. It sucks fresh air through the crankcase, which picks up the vapors and directs them through a metering device called the PCV valve and into the intake manifold to be burnt in the combustion chamber.
At maximum vacuum (idle), the PCV valve opens only a little bit to allow some flow of gases into the intake with vacuum pressure. As you accelerate, vacuum decreases, which causes the PCV valve to open further and allow more gases into the intake. Since the PCV introduces unmetered air, it is often called a “controlled vacuum leak.” The Mass Air Flow (MAF) sensor accounts for the PCV’s metered air entry. A faulty PCV does not meter crankcase vapors correctly and usually results in too much vapor getting into the intake, thus ruining fuel economy and disrupting the air/fuel ratio among other things.
Under boost, the PCV valve closes completely. If it were open, boost pressure would get into the crankcase and wreak havoc on the seals. So how do the gases escape the crankcase under boost? Through a valve cover vent hose that returns the gases to the area in front of the turbocharger where they enter the intake system.
There are two main PCV system modifications: (1) A check valve in the vacuum line preceding the PCV valve to prevent boost from leaking past a faulty PCV valve and into the crankcase. (2) Valve cover breathers to filter and then release blowby gases into the atmosphere and prevent oil vapor from going into the turbo.
At maximum vacuum (idle), the PCV valve opens only a little bit to allow some flow of gases into the intake with vacuum pressure. As you accelerate, vacuum decreases, which causes the PCV valve to open further and allow more gases into the intake. Since the PCV introduces unmetered air, it is often called a “controlled vacuum leak.” The Mass Air Flow (MAF) sensor accounts for the PCV’s metered air entry. A faulty PCV does not meter crankcase vapors correctly and usually results in too much vapor getting into the intake, thus ruining fuel economy and disrupting the air/fuel ratio among other things.
Under boost, the PCV valve closes completely. If it were open, boost pressure would get into the crankcase and wreak havoc on the seals. So how do the gases escape the crankcase under boost? Through a valve cover vent hose that returns the gases to the area in front of the turbocharger where they enter the intake system.
There are two main PCV system modifications: (1) A check valve in the vacuum line preceding the PCV valve to prevent boost from leaking past a faulty PCV valve and into the crankcase. (2) Valve cover breathers to filter and then release blowby gases into the atmosphere and prevent oil vapor from going into the turbo.