Chrysler Full-Size Vans 1967-1988 Repair Guide

Positive Crankcase Ventilation System



See Figures 1 and 2

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Fig. Fig. 1: Common inline 6-cylinder engine PCV system

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Fig. Fig. 2: Common V8 engine PCV system

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 the gases which are formed in the combustion chamber leak by the piston rings and enter the crankcase. Since these gases are under pressure they tend to escape from the crankcase and enter into the atmosphere. If these gases are allowed to remain in the crankcase for any length of time, they would contaminate the engine oil and cause sludge to build up. If the gases are allowed to escape into the atmosphere, they would pollute the air, as they contain unburned hydrocarbons. The crankcase emission control equipment recycles these gases back into the engine combustion chamber, 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. 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.

The above explanation and the troubleshooting procedure which follows applies to all of the gasoline engines installed in these trucks, since all are equipped with PCV systems.


See Figure 3

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Fig. Fig. 3: Place your finger over the valve to check for vacuum

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 and a strong vacuum should be felt when you place a finger over the valve inlet if the valve is working properly. While you have your finger over the PCV valve inlet, check for vacuum leaks in the hose and at the connections.

When the PCV valve is removed 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.


See Figures 4, 5 and 6

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Fig. Fig. 4: To change the crankcase inlet air filter, remove the air cleaner housing-to-filter hose ...

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Fig. Fig. 5: ... then pull the filter from the retaining grommet in the rocker cover

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Fig. Fig. 6: Pull the hose (A) off the PCV valve, then remove the valve from the rocker arm grommet (B)

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

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