GM Astro/Safari 1985-1996 Repair Guide

Positive Crankcase Ventilation (PCV)


See Figure 1

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Fig. Fig. 1: Typical air and vapor flow through PCV systems

The Positive Crankcase Ventilation (PCV) system is used to vent pressure which builds in the crankcase during engine operation. Fresh air is inducted to the crankcase through the ventilation system (which may include a separate filter in the air cleaner on some models) and is then drawn to the engine intake air system so it can be burned. The PCV valve may be the most important part of the system since it regulates the flow of the vapors during engine operation. If the valve becomes stuck open it could allow vapors to enter the intake at the wrong time (causing poor driveability). If is becomes stuck closed or clogged, it could allow excessive crankcase pressure to cause gasket leaks and/or the buildup of damaging sludge in the crankcase oil. In any case, it is an inexpensive part which should NOT be overlooked for periodic inspection and replacement.

The PCV valve is usually attached to a valve cover by a rubber grommet and connected to the intake manifold through a ventilation hose. Replace the PCV valve and the PCV filter (located in the air cleaner on TBI and carbureted models so equipped) every 30,000 miles (48,000 km).


See Figures 2 and 3

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Fig. Fig. 2: The PCV valve is normally fitted to a rubber grommet in the valve cover

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Fig. Fig. 3: Once it is removed from the grommet, carefully pull it free of the vacuum hose

  1. Open the hood to see if access is possible without removing the engine cover. Depending on your model (and the length of your arms) you may be able to reach the valve for replacement. If not, SORRY, but you will have to remove the engine cover for better access.
  3. Pull the PCV from the valve cover grommet and disconnect it from the ventilation hose(s).
  5. You can inspect the valve for operation: (1) Shake it to see if the valve is free; (2) Blow through it (air will pass in one direction only). If you have removed the engine cover, take this opportunity to also check the condition of the vacuum hose and, if applicable, the filter in the air cleaner housing and replace any damaged or worn component.

When replacing the PCV valve, it is recommended to use a new one. It is usually an inexpensive part, but it performs a very important function for the life of your engine's gaskets and oil.

  1. Upon installation, be sure the valve seats properly in the valve cover grommet and that the vacuum hose is tight on the valve fitting.