Ford- Fairmount/Zephyr 1978-1983 Repair Guide

Positive Crankcase Ventilation (PCV) System



Click image to see an enlarged view

Fig. Fig. 1 Typical Positive Crankcase Ventilation (PCV) system component identification

Click image to see an enlarged view

Fig. Fig. 2 To remove the PCV valve, pull it out of the grommet (arrow) and detach all vacuum hoses

Click image to see an enlarged view

Fig. Fig. 3 Inspect the fresh air breather filter, mounted in the air cleaner, when checking the PCV system

All Fairmonts and Zephyrs are equipped with a Positive Crankcase Ventilation (PCV) system to control crankcase blow-by vapors. The system consists of a PCV valve and an oil separator mounted on top of the valve cover or on the side of the engine block, a non-ventilated oil filter cap and a pair of hoses supplying filtered intake air to the valve cover and delivering the crankcase vapors from the valve cover to the intake manifold or carburetor.

The system functions as follows: when the engine is running, a small portion of the gases which are formed in the combustion chamber leaks past the piston rings and enters 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.

These crankcase (blow-by) vapors 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 the gases 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 is 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 the 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.


With the engine running, pull the PCV valve and hose from the oil separator. Block off the end of the valve with your finger. Engine speed should drop at least 50 rpm when the end of the valve is blocked. If engine speed does not drop at least 50 rpm, the valve is defective and should be replaced.


  1. Remove the PCV system components, filler cap, PCV valve, hoses, tubes, fittings, etc. from the engine.
  3. Soak the rubber ventilation hose(s) in a low volatility petroleum base solvent.
  5. Clean the rubber ventilation hose(s) by passing a suitable cleaning brush through them.
  7. Thoroughly wash the rubber hoses in a low volatility petroleum base solvent and dry with compressed air.
  9. Thoroughly wash the crankcase breather cap, if so equipped, in a low volatility petroleum base solvent and shake dry. Do not dry with compressed air; damage to the filtering media may result.
  11. Thoroughly clean tubes, fittings, connections to assure unobstructed flow of emission gases.
  13. Install a new PCV valve and reinstall previously removed hoses, tubes, fittings, etc. to their proper location.
  15. Replace any system component that shows signs of damage, wear or deterioration as required.
  17. Replace any hose or tube that cannot be cleaned satisfactorily.