Cherokee, Grand Cherokee, 1999-2005

Positive Crankcase Ventilation System

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Description & Operation



The 4.7L V-8 engine is equipped with a closed crankcase ventilation system and a Positive Crankcase Ventilation (PCV) valve. This system consists of:



PCV valve mounted to the oil filler housing. The PCV valve is sealed to the oil filler housing with an O-ring.
 
Air cleaner housing
 
Interconnected breathers (two) threaded into the rear of each cylinder head.
 
Tubes and hose to connect the system components.
 

The PCV system operates by engine intake manifold vacuum. Filtered air is routed into the crankcase through the air cleaner hose and crankcase breathers. The metered air, along with crankcase vapors, is drawn through the PCV valve and into a passage in the intake manifold. The PCV system manages crankcase pressure and meters blow-by gases to the intake system, reducing engine sludge formation.

The PCV valve contains a spring-loaded plunger. This plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum.

When the engine is not operating, or during an engine pop-back, the spring forces the plunger back against the seat. This will prevent vapors from flowing through the valve. During periods of high manifold vacuum, such as idle or cruising speeds, vacuum is sufficient to completely compress spring. It will then pull the plunger to the top of the valve. In this position there is minimal vapor flow through the valve. During periods of moderate manifold vacuum, the plunger is only pulled part way back from inlet. This results in maximum vapor flow through the valve.

Diagnosis & Testing



  1. Disconnect PCV line/hose by disconnecting rubber connecting hose at PCV valve fitting.
  2.  
  3. Remove PCV valve at oil filler tube by rotating PCV valve downward until locating tabs have been freed at cam lock. After tabs have cleared, pull valve straight out from filler tube.
    WARNING
    To prevent damage to PCV valve locating tabs, valve must be pointed downward for installation. Do not force valve from oil filler tube.

  4.  
  5. After valve is removed, check condition of valve O-ring. Also, PCV valve should rattle when shaken.
  6.  
  7. Reconnect PCV valve to its connecting line/hose. Start engine and bring to idle speed.
  8.  
  9. If valve is not plugged, a hissing noise will be heard as air passes through valve. Also, a strong vacuum should be felt with a finger placed at valve inlet.
  10.  
  11. If vacuum is not felt at valve inlet, check line/hose for kinks or for obstruction. If necessary, clean out intake manifold fitting at rear of manifold. Do this by turning a 1/4-inch drill (by hand) through the fitting to dislodge any solid particles. Blow out the fitting with shop air. If necessary, use a smaller drill to avoid removing any metal from the fitting.
    WARNING
    Do not attempt to clean the old PCV valve.

  12.  
  13. Return PCV valve back to oil filler tube by placing valve locating tabs into cam lock. Press PCV valve in and rotate valve upward. A slight click will be felt when tabs have engaged cam lock. Valve should be pointed towards rear of vehicle.
  14.  
  15. Connect PCV line/hose and connecting rubber hose to PCV valve.
  16.  
  17. Disconnect rubber hose from fresh air fitting at left side of air cleaner resonator box. Start engine and bring to idle speed. Hold a piece of stiff paper (such as a parts tag) loosely over the opening of the disconnected rubber hose.
  18.  
  19. The paper should be drawn against the hose opening with noticeable force. This will be after allowing approximately one minute for crankcase pressure to reduce.
  20.  
  21. If vacuum is not present, disconnect each PCV system hose at top of each breather. Check for obstructions or restrictions.
  22.  
  23. If vacuum is still not present, remove each PCV system breather from each cylinder head. Check for obstructions or restrictions. If plugged, replace breather. Tighten breather to 12 Nm (106 inch lbs.) torque. Do not attempt to clean breather
  24.  
  25. If vacuum is still not present, disconnect each PCV system hose at each fitting and check for obstructions or restrictions.

    Click image to see an enlarged view

    Fig.

  26.  

Positive Crankcase Ventilation (PCV) Valve

The PCV valve is located on the oil filler tube. Two locating tabs are located on the side of the valve. These 2 tabs fit into a cam lock in the oil filler tube. An O-ring seals the valve to the filler tube.

  1. Disconnect PCV line/hose by disconnecting rubber hose at PCV valve fitting.
  2.  
  3. Remove PCV valve at oil filler tube by rotating PCV valve downward (counter-clockwise) until locating tabs have been freed at cam lock. After tabs have cleared, pull valve straight out from filler tube.
    WARNING
    To prevent damage to PCV valve locating tabs, valve must be pointed downward for Removal & Installation. Do not force valve from oil filler tube.

  4.  
  5. After valve is removed, check condition of valve O-ring.
  6.  

To Install:

  1. Return the PCV valve back to oil filler tube by placing valve locating tabs into cam lock.
  2.  
  3. Press the PCV valve in and rotate valve upward. A slight click will be felt when tabs have engaged cam lock. The valve should be pointed towards rear of vehicle.
  4.  
  5. Connect PCV line/hose and rubber hose to PCV valve.

    Click image to see an enlarged view

    Fig.

  6.  

 
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