GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Crankcase Ventilation System

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OPERATION



See Figures 1, 2 and 3

The 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.



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Fig. Fig. 1: The PCV system circulates crankcase vapors into the intake manifold for burning-2.0L and 2.5L engines shown

The CV system, used on the 2.3L, 2.4L and some 2.5L engines, allows crankcase vapors to escape but does not introduce fresh air into the crankcase. However, the CV system on the 3.1L engine, does introduce fresh air into the crankcase.

The PCV system and the CV system on the 3.1L engine, circulates fresh air from the air cleaner or intake duct through the crankcase, where it mixes with blow-by gases and then passes through the Positive Crankcase Ventilation (PCV) valve or constant bleed orifice into the intake manifold.



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Fig. Fig. 2: Cross-section of a PCV valve



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Fig. Fig. 3: The CV system do not use a PCV valve-2.3L engine

When manifold vacuum is high, such as at idle, the orifice or valve restricts the flow of blow-by gases into the intake 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 the manifold. The air cleaner has a small filter attached to the inside wall that connects to the breather hose to trap impurities flowing in either direction.

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.

TESTING



PCV Valve/Constant Bleed Orifice

See Figure 4

  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.  



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Fig. Fig. 4: Check the PCV valve for vacuum at idle

  1. 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.
  2.  

PCV System/CV System-3.1L Engines

  1. Check to make sure the engine has the correct PCV valve or bleed orifice.
  2.  
  3. Start the engine and bring to normal operating temperature.
  4.  
  5. Block off PCV system fresh air intake passage.
  6.  
  7. Remove the engine oil dipstick and install a vacuum gauge on the dipstick tube.
  8.  
  9. Run the engine at 1500 rpm for 30 seconds then read the vacuum gauge with the engine at 1500 rpm.

    If vacuum is present, the PCV system is functioning properly.
     
    If there is no vacuum, the engine may not be sealed and/or is drawing in outside air. Check the grommets and valve cover or oil pan gasket for leaks.
     
    If the vacuum gauge registers a pressure or the vacuum gauge is pushed out of the dipstick tube, check for the correct PCV valve or bleed orifice, a plugged hose or excessive engine blow-by.
     

  10.  

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 inch (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

See Figure 5

  1. Label and remove the PCV valve vacuum hoses 1 from the 3 fuel pressure regulator, and 2 PCV valve.
  2.  



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Fig. Fig. 5: Vacuum hoses (1), fuel pressure regulator (3) and PCV valve (2)

  1. Pull the valve from the valve cover.
  2.  

To install:
  1. Insect the grommet and replace as necessary.
  2.  
  3. Insert the valve into the valve cover and attach all vacuum hoses previously removed.
  4.  

Oil Separator

See Figure 6

  1. Remove the air cleaner outlet resonator.
  2.  
  3. Unbolt and extract the intake manifold. Refer to the procedure in Engine & Engine Overhaul .
  4.  
  5. Label and disconnect all hoses attached to the oil separator.
  6.  
  7. Unbolt the oil separator, then pull the unit from the engine.
  8.  



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Fig. Fig. 6: Oil separator hoses (1 and 4), retaining bolts (2) and oil separator (3)

To install:
  1. Attach the separator to the engine and secure the retaining bolts to 15-18 ft. lbs. (20-28 Nm).
  2.  
  3. Connect all vacuum hoses to the oil, separator. Apply a small amount of liquid soap to the inside of the edges of the hose to ease installation.
  4.  
  5. Install the intake manifold.
  6.  
  7. Connect the air cleaner outlet resonator.
  8.  

 
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