Chrysler Front Wheel Drive Cars 6-CYL 1988-1995 Repair Information

Positive Crankcase Ventilation System


The Premier and Monaco vehicles do not utilize a PCV system, rather these vehicles use a Crankcase Ventilation (CCV) system, which is described later in this section.


See Figures 1, 2, 3 and 4

The Positive Crankcase Ventilation (PCV) system is used to draw the incompletely burned air/fuel mixture that passes the piston rings and valve guides out of the crankcase and valve cover. This mixture contains a great deal of unburned hydrocarbons. The PCV system conducts it to the engine's air intake system for burning with the fresh mixture in the combustion chambers. In this way, total emissions of unburned fuel are greatly reduced.

The system's PCV valve is connected, via a short hose, to the rocker arm cover. The PCV valve itself controls total flow to the system so that, regardless of engine intake vacuum, a stable amount of air will enter the system. The Chrysler system is unique in that it draws fresh air into the PCV circuit without passing it through the engine crankcase.

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Fig. Fig. 1: The route air travels through the PCV system-3.0L engines, except Premier and Monaco

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Fig. Fig. 2: The PCV valve is mounted in the lower intake manifold and attached to the rocker arm cover with a rubber hose-3.0L engines, except Premier and Monaco

The fuel injection system is precisely calibrated to compensate for the extra air the system introduces into the engine's combustion chambers. At the same time, because of the high vacuum the system operates under, the potential exists for it to bleed a great deal of excess air into the system and disturb the mixture. If the engine runs poorly, especially at idle speeds (when vacuum is highest), inspect the PCV system thoroughly for leaks and the PCV valve for clogging or sticking. The valve may be clogged (stuck partly open), so that too much excess air can enter the system, which creates a lean mixture.

Since the PCV system removes vapors from the crankcase that, if left there, could condense and contribute significantly to engine wear, effective maintenance can improve both engine performance and longevity. If there are otherwise unexplained oil leaks through seals or if crankcase vapors are expelled into the engine compartment, check the system for clogged hoses or a PCV valve that is stuck shut or clogged. see General Information & Maintenance for basic maintenance and PCV valve tests.

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Fig. Fig. 3: The fresh air hose for the PCV system is attached to the passenger's side of the air cleaner box-3.0L engines, except Premier and Monaco

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Fig. Fig. 4: On the 3.3L and 3.8L engines, the PCV valve is mounted between the valve cover and crankcase vent vacuum hoses

With the engine idling, remove the PCV valve from the engine. If the valve is operating properly, a hissing noise will be heard and a strong vacuum felt when a finger is placed over the valve inlet. With the engine OFF, the valve should rattle when it is shaken. If the valve is not operating properly it must be REPLACED. Do not attempt to clean the old PCV valve.


See Figures 1 through 5

To inspect the PCV valve, remove the valve from the lower intake manifold (3.0L engines) or from between the crankcase vent hose and the rocker arm cover hose (3.3L and 3.8L engines), 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. 5: Check for suction at the PCV valve while the vehicle is idling