GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Positive Crankcase Ventilation (PCV) Valve

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See Figures 1 and 2

The PCV system must be operating properly in order to allow evaporation of fuel vapors and water from the crankcase. This system should be serviced and both the PCV valve and filter replaced as outlined in the maintenance interval charts at the end of this section. Normal service entails cleaning the passages of the system hoses with solvent, inspecting them for cracks and breaks, and replacing them as necessary. The PCV valve contains a check valve and, when working properly, this valve will make a rattling sound when the outside case is tapped. If it fails to rattle, then it is probably stuck in a closed position and needs to be replaced.



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Fig. Fig. 1: PCV flow through the engine



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

The PCV system is designed to prevent the emission of gases from the crankcase into the atmosphere. It does this by connecting a crankcase outlet (usually the valve cover) to the intake with a hose. The crankcase gases travel through the hose to the intake where they are returned to the combustion chamber to be burned. If maintained properly, this system reduces condensation in the crankcase and the resultant formation of harmful acids and oil dilution. Disconnect the valve from the engine or merely clamp the hose shut. The PCV valve is an inexpensive item and it is suggested that it be replaced, if suspected. If the new valve doesn't noticeably improve engine idle, the problem might be a restriction in the PCV hose. For further details on PCV valve operation please refer to Fuel System of this repair guide.

FUNCTIONAL CHECK



See Figures 3, 4, 5, and 6



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Fig. Fig. 3: PCV system-4.3L TBI engine



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Fig. Fig. 4: PCV system-2.2L MFI engine



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Fig. Fig. 5: PCV system-4.3L CMFI engine



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Fig. Fig. 6: PCV system-4.3L CSFI engine

If the engine is idling rough, check for a clogged PCV valve, dirty vent filter or air cleaner element, or plugged hose. Test the system using the following procedure and replace components as necessary.

  1. Remove the PCV valve from the rocker cover.
  2.  
  3. Run the engine at idle and place your thumb over the end of the valve to check for vacuum. If the engine speed decreases less than 50 rpm, the valve is clogged and should be replaced. If the engine speed decreases much more than 50 rpm, then the valve is good.
  4.  
  5. If no vacuum exists, check for plugged hoses, manifold port.
  6.  
  7. To check the PCV valve, remove the valve from the hose and shake it. If a rattling noise is heard, the valve is good. If no noise is heard, the valve is plugged and replacement is necessary.
  8.  

REMOVAL & INSTALLATION



See Figures 7 and 8



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Fig. Fig. 7: Remove the PCV valve from the valve cover



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Fig. Fig. 8: Removing the PCV valve from the hose

  1. Grasp the valve and withdraw it from the valve cover.
  2.  
  3. Holding the valve in one hand and the hose in the other, carefully pull the valve from the hose and remove from the vehicle.
  4.  

Some PCV valve hoses will be retained to the valve using a clamp. If so, use a pair of pliers to slide the clamp back on the hose until it is clear of the bulged area on the end of PCV valve nipple. With the clamp in this position, the hose should be free to slip from the valve.

To install:
  1. Install the PCV hose to the grommet in the valve cover.
  2.  
  3. Connect the PCV hose to the valve.
  4.  

 
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