GM Malibu/Cutlass 1997-2000

Crankcase Ventilation System

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OPERATION



A Crankcase Ventilation (CV) system is used on all vehicles to evacuate the crankcase vapors. There are 2 types of ventilation systems: Crankcase Ventilation (CV) and Positive Crankcase Ventilation (PCV). Both systems purge crankcase vapors and differ only in the use of fresh air.

The CV system, used on the 2.4L engine, allows crankcase vapors to escape but does not introduce fresh air into the crankcase. The blow-by vapors are drawn into the oil/air separator through a hose from the timing chain housing. Crankcase vapors are passed through the oil/air separator into the air cleaner outlet resonator. The oil/air separator is attached to the engine block and returns any oil suspended in the blow-by vapors to the crankcase. These blow-by gases will then be mixed with the intake air in the air cleaner outlet resonator instead of the manifold. The blow-by vapors are then drawn into the engine by normal engine vacuum and burned by the combustion process.

The 3.1L engine is equipped with a Positive Crankcase Ventilation (PCV) system to control crankcase blow-by vapors. The PCV system is used to evacuate the crankcase vapors. Fresh air from the air cleaner is supplied to the crankcase, mixed with blow-by gases and then passed through a Positive Crankcase Ventilation (PCV) valve into the intake manifold. When manifold vacuum is high, such as at idle, the orifice or valve restricts the flow of blow-by gases allowed into the manifold. If abnormal operating conditions occur, the system will allow excessive blow-by gases to back flow through the hose into the air cleaner. These blow-by gases will then be mixed with the intake air in the air cleaner instead of in the manifold.

A plugged PCV valve, orifice or hose may cause rough idle, stalling or slow idle speed, oil leaks, oil in the air cleaner or sludge in the engine. A leak could cause rough idle, stalling or high idle speed. The condition of the grommets in the valve cover will also affect system and engine performance.



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Fig. Cross-section of a PCV valve



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Fig. When inspecting or removing the PCV valve, be sure to inspect the condition of the hose end and grommet for cracking, dry rot, or swelling-3.1L engine shown



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Fig. When removing the PCV valve, be sure to wipe excess oil from the grommet's inside surface

TESTING



CV System-2.4L engine


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Fig. Exploded view of the oil separator mounting-2.4L engine

  1. Check the CV system for proper flow by looking for oil sludging or leaks.
  2.  
  3. If noted, check the smaller nipple of the oil/air separator by blowing through it or inserting a 0.06 in. (1.52mm) gauge plug into the orifice inside the nipple.
  4.  
  5. If the orifice is plugged, replace the CV oil/air separator assembly.
  6.  

PCV System-3.1L Engine


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Fig. Check the PCV valve for vacuum at idle

  1. Run the engine at idle at normal operating temperature.
  2.  
  3. Remove the PCV valve or orifice from the grommet in the valve cover and place your thumb over the end to check if vacuum is present. If vacuum is not present, check for plugged hoses or manifold port. Repair or replace as necessary.
  4.  
  5. If the engine is equipped with a PCV valve, stop the engine and remove the valve. Shake and listen for the rattle of the check valve needle. If no rattle is heard, replace the valve.
  6.  

REMOVAL & INSTALLATION



For removal and installation of the PCV valve and CV system oil/air separator, refer to of this guide.

 
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