Jeep Wagoneer/Commando/Cherokee 1984-1998

Crankcase Ventilation System (PCV/CCV)



Crankcase emission control equipment is separated into two different systems: Positive Crankcase Ventilation (PVC) and Crankcase Ventilation System (CCV). The systems perform the same function, differing only in the way the exhaust gases are metered. The PVC system uses a valve, containing spring loaded plunger, which meters the amount of crankcase vapors routed to the combustion chamber based on manifold vacuum. The CCV system contains a metered orifice of a calibrated size which meters the amount of crankcase vapors drawn from the engine based on manifold vacuum.

When the engine is running, a small portion of the gases which are formed in the combustion chamber during combustion 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 were allowed to remain the 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.

While the engine is running, clean filtered air is drawn into the crankcase either directly through the oil filler cap, or through a filter mounted in the air cleaner assembly and connected to the oil filler cap. As the air passes through the crankcase it picks up combustion gases, carries them out of the crankcase, through the PCV valve, and into the intake manifold. After entering the intake manifold gases are drawn into the combustion chamber and burned.

The most critical component in the system is the metering device-the PCV valve in the PVC system, or the metered orifice in the CCV system-which controls the amount of gases recycled into the combustion chamber. If the metering device should become clogged, gases will be prevented from escaping the crankcase by the normal route. Since the gases are under pressure, they will find a point of least resistance, usually a weak oil seal or gasket, and create an oil leak. In addition to creating oil leaks, clogged ventilation systems also allow gases to remain in the crankcase for an extended period of time. This promotes the formation of sludge in the engine and ultimately leads to decreased engine life.


PCV Valve

See Figure 1

To inspect the PCV valve, remove the valve from the rocker arm cover hose, then shake it. If the valve rattles, it is probably fine; if there is no sound, it must be replaced and the PCV hose cleaned by spraying solvent (such as a carburetor cleaner type of solvent) through it.

If the valve rattles, you should still check the PCV valve with the engine idling. Pull it out of the vent module and place your finger or thumb over the end to stop air flow. You should feel some suction, and the engine speed should drop slightly. If there is no suction, or if the engine idle speeds up and smooths out considerably, replace the valve. Remove the PCV hose from the engine, then inspect it and, if the inside is coated with gum and varnish, clean it by spraying solvent through it.

Check the vacuum at the PCV inlet (from the rocker arm cover to the air cleaner) tube, as well. Disconnect this tube from the air cleaner and loosely hold a piece of paper over the tube. After a few seconds (10-15 seconds), enough vacuum should build up to cause the paper to be sucked against the opening with a noticeable amount of force. This test proves whether or not the suction side of the system is clear.

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Fig. Fig. 1: View of common PCV valve operation

CCV Fitting

See Figures 2 and 3

  1. With the engine running, remove the CCV fitting.
    1. If the fitting is not plugged, a hissing noise will be heard as air passes through the valve. A strong vacuum should also be felt when a finger is placed over the fitting.
    3. Install the CCV fitting.
    5. Remove the fresh air hose from the air cleaner assembly and loosely hold a piece of paper over the open end of the hose. After allowing about one minute for the crankcase pressure to reduce, the paper should be sucked against the opening with a noticeable amount of force.

  3. Turn the engine OFF . Remove the metered orifice fitting, and check for a plugged condition. A clicking noise should be heard to indicate that the valve mechanism is free.
  5. If the crankcase ventilation system meets the tests in Steps 1 and 2 above, no further service is required. If not, the CCV fitting must be cleaned and the system checked again.
  7. If Step 1c fails when the CCV fitting is cleaned, it will be necessary to replace the molded vacuum hose with a new one, and to clean the metered orifice port.
  9. Clean or replace the engine air cleaner filter element with a new one-for more details, refer to the air cleaner procedure located in General Information & Maintenance .

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Fig. Fig. 2: CCV system diagram for 4.0L engine

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Fig. Fig. 3: CCV system diagram for the 2.5L engine

Removal & Installation

Refer to Routine Maintenance for the PCV valve removal/installation procedure.