GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

Crankcase Ventilation System - Gasoline Engines



All these gasoline vehicles are equipped with a positive crankcase ventilation (PCV) system to control crankcase blow-by vapors. The system functions as follows:

When the engine is running, a small portion of the gases which are formed in the combustion chamber leak by the piston rings and enter the crankcase. Since these gases are under pressure, they tend to escape from the crankcase and enter the atmosphere. If these gases are allowed to remain in the crankcase for any period of time, they contaminate the engine oil and cause sludge to build up in the crankcase. If the gases are allowed to escape into the atmosphere, they pollute the air with unburned hydrocarbons.

The job of the crankcase emission control equipment is to recycle these gases back into the engine combustion chamber where they are reburned.

The crankcase (blow-by) gases are recycled in the following way: as the engine is running, clean, filtered air is drawn through the air filter and into the crankcase. As the air passes through the crankcase, it picks up the combustion gases and carries them out of the crankcase, through the oil separator, through the PCV valve, and into the induction system. As they enter the intake manifold, they are drawn into the combustion chamber where they are reburned.

The most critical component in the system is the PCV valve. This valve controls the amount of gases which are recycled into the combustion chamber. At low engine speeds, the valve is partially closed, limiting the flow of gases into the intake manifold. As engine speed increases, the valve opens to admit greater quantities of gases into the intake manifold. If the valve should become blocked or plugged, the gases will be prevented from escaping from the crankcase by the normal route. Since these gases are under pressure, they will find their own way out of the crankcase. This alternate route is usually a weak oil seal or gasket in the engine. As the gas escapes by the gasket, it also creates an oil leak. Besides causing oil leaks, a clogged PCV valve also allows these gases to remain in the crankcase for an extended period of time, promoting the formation of sludge in the engine.


Inspect the PCV system hose and connections at each tune-up and replace any deteriorated hoses. Check the PCV valve at every tune-up and replace it at 30,000 mile (48,900km) intervals.

  1. Remove the PCV valve from the rocker arm cover.
  3. Start engine, allow to reach normal temperature and idle speed.
  5. Place your thumb over the end of the valve to check for vacuum. If no vacuum, check the valve and hose. Most likely the hose is plugged up.
  7. Newer computer controlled vehicles may no show much of a change in engine rpm when the valve is blocked or removed due to the computer compensating almost instantly to the vacuum change.
  9. Remove the valve from the engine and hose. Shake the valve; it should rattle. If not, it's plugged up with dirt and must be replaced.
  11. When replacing a PCV valve, you MUST use the correct valve. Many valves look alike on the outside, but have different mechanical values. Putting an incorrect PCV valve on a vehicle can cause a great deal of driveability problems. The engine computer assumes the valve is the correct one and may overadjust ignition timing or fuel mixture.


PCV Valve

See Figures 1 and 2

The valve is located in a rubber grommet in the valve cover, connected to the air cleaner housing by a large diameter rubber hose. In replacing the PCV valve, make sure it is fully inserted in the hose, that the clamp is moved over the ridge on the valve so that the valve will not slip out of the hose, and that the valve is fully inserted into the grommet in the valve cover.

Click image to see an enlarged view

Fig. Fig. 1: PCV system operation

  1. Pull the valve (with the hose attached) from the rubber grommet in the valve cover.
  3. Remove the valve from the hose.
  5. Inspect the rubber grommet that houses the valve for deterioration, and replace if necessary.

Click image to see an enlarged view

Fig. Fig. 2: Remove the PCV valve, inspect and replace it if necessary

To install:
  1. Install the new (or reusable) PCV valve into the hose.
  3. Press the valve back into the rubber grommet in the valve cover.

PCV Filter

The PCV filter is located in the air cleaner housing and must be replaced every 50,000 miles (80,000 km).

  1. Remove the air cleaner housing lid.
  3. Slide back the filter retaining clip and remove the old filter.
  5. Install the new filter, replace the retaining clip and replace the housing lid.