GMC 25043669 Valve, Crankcase Vent (Pcv)

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To solve this problem, the positive crankcase ventilation (PCV) system circulates fresh air through the crankcase in order to pick up blow-by gases, which are then rerouted back to the engine through a carburetor. Vacuum hoses and a PCV valve, which regulate the flow of gases according to engine speed and manifold vacuum, are the main components of this system. Carbon and gunk that accumulate in the PCV valve and hoses over time may cause them to jam, hence regular scrutiny is needed to ensure they function properly. Poor idling or reduced idle speed may indicate a restricted or stopped flow in the system. To test for proper vacuum pull off the top plate of the air cleaner and remove the hose leading to the small PCV filter. While your engine is idling put your thumb slightly on towards the end of this hose. A feeling as if there is a slight pull or suction tells that air is being drawn through it. If any vacuum is felt there should be further checks since low or no vacuum will mean that blocking has taken place within this system. By shaking it you can check whether the PCV valve clicks; if it does not, it should be replaced because its check needle does not work properly anymore. When running at idle speed with valve removed, engine should result in a relatively strong vacuum pressure. If there's no or very little difference felt in terms of vacuum pressure either way it might indicate blocked vacuum hose or inlet fitting at engine manifold. Clearing out passages clogged at manifold or carburetor require thorough cleaning, while failure of pcv valve necessitates replacement thereof. When buying a new one for your engine just make sure that you don't get something else instead of genuine PCV valves.

To remove and install the PCV valve, pull the valve and hose straight out of the valve cover or manifold. Use pliers to slide the hose clamp, if equipped, down the hose and off the valve connector. Twist the valve gently to loosen it from the hose and remove it. Inspect the hose and valve cover grommet, and replace them if they are hard, brittle, or cracked. Clean the hose with solvent if it is clogged. Install the valve into the hose, ensuring it seats fully. Attach the hose clamp, if equipped, around the valve assembly. Finally, install the PCV valve in the grommet, making sure it seats fully in the cover grommet.

The PCV valve is located on a rocker arm cover.

To replace the PCV valve, first, pull the valve (with the hose attached) from the rubber grommet in the rocker arm cover or manifold. Then, loosen the retaining clamp and remove the PCV valve from the end of the hose, taking note of its installed position and direction. Compare the old valve with the new one to ensure that they are the same. Push the new valve into the end of the hose until it is properly seated, and then reinstall the clamp. Inspect the rubber grommet for any damage and replace it with a new one if necessary. Finally, securely push the PCV valve and hose into position.

The PCV valve is typically located in one of the rocker arm covers on the side of the engine.

Locate the PCV valve in the valve cover or intake manifold behind the throttle body on 3.4L engines. While the engine is idling at normal operating temperature, remove the valve from its rubber grommet. Cover the valve's end with your finger and check for vacuum. If there's no vacuum, inspect for blockages in the hose, manifold port, or the valve itself. Replace any obstructed or deteriorated hoses. Turn off the engine, shake the PCV valve, and listen for a rattle. If there's no rattle, replace it.

Inspect the rubber grommet at the rocker arm cover for damage and replace it with a new one if needed.