Chrysler Full-Size Trucks 1967-1988 Repair Guide

Positive Crankcase Ventilation System

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See Figures 1, 2, 3 and 4

All gasoline engines covered by this information are equipped with PCV systems.

The crankcase emission control equipment consists of a Positive Crankcase Ventilation (PCV) valve, a closed oil filler cap and the hoses that connect this equipment.

When the engine is running, a small portion of gases which are formed in the combustion chamber leak by the piston rings entering the crankcase. Since these gases are under pressure they tend to escape the crankcase and enter into the atmosphere. If the gases are allowed to remain in the crankcase for any length of time, they would contaminate the engine oil and cause sludge to build. If the gases are allowed to escape into the atmosphere, they would pollute the air, as they contain unburned hydrocarbons. The crankcase ventilation system recycles these gases back into the combustion chambers, where they are burned.

Crankcase gases are recycled in the following manner. While the engine is running, clean filtered air is drawn into the crankcase through the intake air filter and then through a hose leading to the oil filler cap. As the air passes through the crankcase it picks up the combustion gases and carries them out of the crankcase, up through the PCV valve and into the intake manifold. After they enter the intake manifold they are drawn into the combustion chamber and are burned.

The most critical component of the system is the PCV valve. This vacuum-controlled valve regulates the amount of gases which are recycled into the combustion chamber. At low engine speeds the valve is partially closed, limiting the flow of gases into the intake manifold. As engine speed increases, the valve opens to admit greater quantities of the gases into the intake manifold.



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Fig. Fig. 1: Common six cylinder PCV system



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Fig. Fig. 2: Common V8 PCV system



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Fig. Fig. 3: Fully closed crankcase ventilation system on 1967 6-225 and 8-318



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Fig. Fig. 4: Partially closed crankcase ventilation system on 1967 6-225 and 8-318 and 8-383

If the valve should become blocked or plugged, the gases will be prevented from escaping the crankcase by the normal route. Since these gases are under pressure, they will find their own way out of the crankcase. This alternate route is usually a weak oil seal or gasket in the engine. As the gas escapes by the gasket, it also creates an oil leak. Besides causing oil leaks, a clogged PCV valve also allows these gases to remain in the crankcase for an extended period of time, promoting the formation of sludge in the engine.

TROUBLESHOOTING



See Figures 5 and 6

With the engine running, pull the PCV valve and hose from the valve rocker cover rubber grommet.

A hissing noise should be heard as air passes through the valve. If the valve is working properly, a strong vacuum should be felt when you place a finger over the valve inlet. While you have your finger over the PCV valve inlet, check for vacuum leaks in the hose and at the connections.



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Fig. Fig. 5: Place your finger over the valve to check for vacuum

If the PCV valve is disconnected from the engine, a metallic clicking noise should be heard when it is shaken. This indicates that the metal check ball inside the valve is still free and is not gummed up. If no noise is heard, clean or replace the valve. Since these valves are normally inexpensive components, it would probably be smartest to replace the valve if it is suspect.



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Fig. Fig. 6: Common PCV location

REPLACEMENT



  1. Pull the PCV valve and hose from the rubber grommet in the rocker cover.
  2.  
  3. Remove the PCV valve from the hose.
  4.  
  5. Inspect the inside of the valve hose. If it is dirty, disconnect it from the intake manifold and clean it in a suitable, safe solvent.
  6.  

To install:
  1. If the PCV valve hose was removed, connect it to the intake manifold.
  2.  
  3. Connect the PCV valve to its hose.
  4.  
  5. Install the PCV valve into the rubber grommet in the valve rocker cover.
  6.  

 
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