GM Full Size Vans 1987-1997 Repair Guide

PCV Valve

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See Figures 1 and 2

Diesel engines do not utilize a PCV system.

The PCV valve, which is the heart of the positive crankcase ventilation system, should be changed as noted in the Maintenance Intervals chart at the end of this section. The main thing to keep in mind is that the valve should be free of dirt and residue and should be in working order. As long as the valve is not showing signs of becoming damaged or gummed up, it should perform its function properly. When the valve becomes sticky and will not operate freely, it should be replaced.



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Fig. Fig. 1: PCV valve location - 4.3L, 5.0L and 5.7L engines



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Fig. Fig. 2: PCV valve location - 7.4L engine

The PCV valve is used to control the rate at which crankcase vapors are returned to the intake manifold. The action of the valve plunger is controlled by intake manifold vacuum and the spring. During deceleration and idle, when manifold vacuum is high, it overcomes the tension of the valve spring and the plunger bottoms in the manifold end of the valve housing. Because of the valve construction, it reduces, but does not stop, the passage of vapors to the intake manifold. When the engine is lightly accelerated or operated at constant speed, spring tension matches intake manifold vacuum pull and the plunger takes a mid-position in the valve body, allowing more vapors to flow into the manifold.

The valve is either mounted on the valve cover or in the line which runs from the intake manifold to the crankcase. Do not attempt to adjust or repair the valve. If the valve is faulty, replace it.

TESTING



See Figure 3

An inoperative PCV system will cause rough idling, sludge and oil dilution. In the event of erratic idle, never attempt to compensate by disconnecting the PCV system. Disconnecting the PCV system will adversely affect engine ventilation. It could also shorten engine life through the buildup of sludge.

  1. Remove the engine cover located between the driver and passenger seats. Refer to Body & Trim for this procedure.
  2.  
  3. With the engine idling, remove the PCV valve from the rocker cover or line. If the valve is not plugged, a hissing sound will be heard. A strong vacuum should be felt when you place your finger over the valve.
  4.  
  5. Reinstall the PCV valve and allow about a minute for pressure to drop.
  6.  
  7. Remove the crankcase intake air cleaner. Cover the opening in the rocker cover with a piece of stiff paper. The paper should be sucked against the opening with noticeable force.
  8.  
  9. With the engine stopped, remove the PCV valve and shake it. A rattle or clicking should be heard to indicate that the valve is free.
  10.  



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Fig. Fig. 3: Checking the vacuum at the PCV valve

  1. If the system performs as indicated in Steps 2, 3, 4 and 5, no further service is required, unless replacement is specified in the Maintenance Intervals Chart. If the system does not pass these tests, the valve should be replaced with a new one.
  2.  

Do not attempt to clean a PCV valve.

  1. After checking and/or servicing the Crankcase Ventilation System, any components that do not allow passage of air to the intake manifold should be replaced.
  2.  

REMOVAL & INSTALLATION



  1. Remove the engine cover located between the driver and passenger seats. Refer to Body & Trim for this procedure.
  2.  
  3. Remove the PCV valve from the cylinder head cover or from the manifold-to-crankcase hose.
  4.  
  5. Visually inspect all hose connections and hoses for cracks, clogs or deterioration and replace as necessary.
  6.  

See Figures 4 and 5



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Fig. Fig. 4: The PCV valve is normally fitted to a rubber grommet in the valve cover



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Fig. Fig. 5: Once it is removed from the grommet, carefully pull it free of the vacuum hose

 
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