Chevrolet Full Size Cars 1979-1989

Positive Crankcase Ventilation (PCV) Valve


The PCV system must be operating properly in order to allow evaporation of fuel vapors and water from the crankcase. This system should be checked and serviced every year or 15,000 miles. The PCV should be replaced every two years or 30,000 miles. Normal service entails cleaning the passages of the system hoses with solvent, inspecting them for cracks and breaks, and replacing them as necessary. The PCV valve contains a check valve and, when working properly, this valve will make a rattling sound when the outside case is tapped. If it fails to rattle, then it is probably stuck in a closed position and needs to be replaced.

The PCV system is designed to prevent the emission of gases from the crankcase into the atmosphere. It does this by connecting a crankcase outlet (usually the valve cover) to the intake manifold with a hose. The crankcase gases travel through the hose to the intake manifold where they are returned to the combustion chamber to be burned. If maintained properly, this system reduces condensation in the crankcase and the resultant formation of harmful acids and oil dilution. A clogged PCV valve will often cause a slow or rough idle due to a richer fuel mixture. A car equipped with a PCV system has air going through a hose to the intake manifold from an outlet at the valve cover. To compensate for this extra air going to the manifold, carburetor specifications require a richer (more gas) mixture at the carburetor. If the PCV valve or hose is clogged, this air doesn't go to the intake manifold and the fuel mixture is too rich. A rough, slow idle results. The valve should be checked before making any carburetor adjustments. Disconnect the valve from the engine or merely clamp the hose shut. If the engine speed decreases less than 50 rpm, the valve is clogged and should be replaced. If the engine speed decreases much more than 50 rpm, then the valve is good. The PCV valve is an inexpensive item and it is suggested that it be replaced. If the new valve doesn't noticeably improve engine idle, the problem might be a restriction in the PCV hose. For further details on PCV valve operation see refer to of this guide.


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Fig. Fig. 1 Remove the PCV valve and hose from the valve cover grommet

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Fig. Fig. 2 Grasp and pull the valve from the hose

  1. Grasp the valve and withdraw it from the valve cover.
  3. Holding the valve in one hand and the hose in the other, carefully pull the valve from the hose and remove from the vehicle.

Some PCV valve hoses will be retained to the valve using a clamp. If so, use a pair of pliers to slide the clamp back on the hose until it is clear of the bulged area on the end of PCV valve nipple. With the clamp in this position, the hose should be free to slip from the valve.

To install:

  1. Check the PCV valve for deposits and clogging. The valve should rattle when shaken. If the valve does not rattle, clean the valve with solvent until the plunger is free or replace the valve.
  3. Install the PCV hose to the grommet in the valve cover.
  5. Connect the PCV hose to the valve.