Chevrolet Citation/Omega/Phoenix/Skylark 1980-1985 Repair Guide

Positive Crankcase Ventilation (PCV) System

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OPERATION





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Fig. Fig. 1 Schematic of a typical PCV system flow



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Fig. Fig. 2 The PCV valve is mounted in the rocker arm (valve) cover

All X-Body cars 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.

COMPONENT TESTING



PCV Valve


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Fig. Fig. 3 Check the PCV valve for vacuum at idle

  1. Remove the PCV valve from the grommet in the rocker arm (valve) cover.
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  3. Start and run the engine at icle.
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  5. Place your thumb over the end of the valve to check for vacuum. If there is no vacuum present at the valve, check for plugged hoses or valve.
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  7. Shut the engine off. Shake the valve and listen for the rattle to check the needle in the valve. If the PCV valve does not rattle, replace the valve.
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SERVICE





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Fig. Fig. 4 PCV valve on a 4-cylinder engine, removed from its hose and valve cover grommet

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 intervals. Replacement procedures are in Section One.

REMOVAL & INSTALLATION



PCV Filter
  1. Slide the rubber coupling that joins the tube coming from the valve cover to the filter off the filter nipple. Remove the air cleaner case lid. Side the spring clamp off the filter, and remove the filter.
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  3. Inspect the rubber grommet in the valve cover and the rubber coupling for brittleness or cracking. Replace parts as necessary.
  4.  
  5. Insert the new PCV filter through the hole in the air cleaner case, with the open portion of the filter upward. Make sure the square portion of the filter behind the nipple fits into the square hole in the air cleaner case.
  6.  
  7. Install a new spring clamp onto the nipple. Make sure that the clamp goes under the ridge on the filter nipple all the way around. Reconnect the rubber coupling and install the cover.
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