GM Cavalier/Sunfire 1995-2000 Repair Guide

Crankcase Ventilation System

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OPERATION



See Figures 1 and 2

A crankcase ventilation 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 2.3L and 2.4L engines, 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 2.2L 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. Fig. 1: Cross-section of a PCV valve



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Fig. Fig. 2: The PCV system circulates crankcase vapors into the intake manifold for burning-2.2L engine shown

TESTING



PCV System

See Figure 3



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Fig. Fig. 3: 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.  

CV System
  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) plug gauge into the orifice inside the nipple.
  4.  
  5. If the orifice is plugged, replace the CV oil/air separator assembly.
  6.  

REMOVAL & INSTALLATION



PCV Valve (2.2L Engine Only)

Removal and installation of the PCV valve refer to General Information & Maintenance of this guide.

Oil/Air Separator (2.3L/2.4L Engines Only)

See Figures 4 and 5



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Fig. Fig. 4: The CV system does not use a PCV valve-2.3L engine shown



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Fig. Fig. 5: The oil separator mounting-2.4L engine

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner outlet resonator.
  4.  
  5. Remove the intake manifold. Refer to Engine and Engine Rebuilding .
  6.  
  7. Label and disconnect the oil/air separator hoses.
  8.  
  9. Remove the oil/air separator mounting bolts.
  10.  
  11. Remove the oil/air separator.
  12.  

To install:
  1. Install the oil/air separator.
  2.  
  3. Tighten the oil/air separator mounting bolts to 15-18 ft. lbs. (20-28 Nm).
  4.  
  5. Connect the oil/air separator hoses.
  6.  
  7. Install the intake manifold.
  8.  
  9. Install the air cleaner outlet resonator.
  10.  
  11. Connect the negative battery cable.
  12.  

 
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