GM Cadillac Deville_Fleetwood_ELD_Seville 1990-1998

Crankcase Ventilation System

Print

A Positive Crankcase Ventilation (PCV) system is used to consume crankcase vapors in the combustion process instead of venting them to the atmosphere. In gasoline engines, a small amount of combustion gases leak past the piston rings into the crankcase. These crankcase blow-by gases contain undesirable hydrocarbon air pollutants. The PCV system is used to prevent these vapors from escaping into the atmosphere, while allowing proper ventilation of the crankcase to maintain good oil quality. Fresh air from the air cleaner is pulled into the crankcase, mixed with blow-by gases and then purged through the Positive Crankcase Ventilation (PCV) valve into the intake manifold.

OPERATION



The primary control is through the PCV valve, which meters the flow rate dependent on intake manifold vacuum.

When intake manifold vacuum is high, during deceleration, low speed driving or idle, the PCV valve controls a low flow rate. This is because during these modes of operation, the crankcase gas levels, including cylinder blow-by, are low.

When intake manifold vacuum is low, such as during acceleration or high load operation, the PCV valve controls flow to a higher rate to accommodate increased engine crankcase gases.

Under full throttle operation or abnormal conditions, such as a worn or damaged engine, or during high speed light load operation, the system allows excess blow-by gases to flow through the fresh air tube into the inlet duct to be combined with incoming air from the air cleaner.



Click image to see an enlarged view

Fig. "Crankcase vapor flow through the PCV system-4.9L engine shown

A plugged PCV valve or hose may cause the following conditions:



Rough idle
 
Stalling or slow idle speed
 
Oil leaks
 
Oil in the air cleaner
 
Sludge in the engine
 

A leaking valve or hose could cause the following conditions:



Erratic idle speed
 
Rough idle
 
Stalling
 



Click image to see an enlarged view

Fig. PCV system operation-4.6L engine



Click image to see an enlarged view

Fig. PCV valve cross section

PCV SYSTEM TESTING



If an engine is idling rough, check for a clogged PCV valve or plugged hose. Replace system components as required.

  1. Remove the PCV valve from the rocker cover.
  2.  
  3. Run the engine at idle.
  4.  
  5. Place your thumb over the end of the valve to check for vacuum. If there is no vacuum at the valve, check for plugged hoses, intake manifold port, or PCV valve. Replace plugged or deteriorated hoses.
  6.  



Click image to see an enlarged view

Fig. PCV hose, air cleaner and grommet on left cam cover-4.6L engine

  1. Turn the engine OFF and remove the PCV valve. Shake the valve and listen for the rattle of the check needle inside the valve. If the valve does not rattle, replace it.
  2.  



Click image to see an enlarged view

Fig. Check the PCV valve for vacuum at idle

REMOVAL & INSTALLATION



  1. Locate the PCV valve on the valve cover or in the intake manifold.
  2.  
  3. Grasp the PCV valve firmly and pull it out of the rubber grommet.
  4.  
  5. Once free of the grommet, disconnect it from the vacuum line.
  6.  

To install:

  1. Inspect the rubber grommet. Replace if necessary.
  2.  
  3. Installation is the reversal of the removal procedure.
  4.  

 
label.common.footer.alt.autozoneLogo