GMC 25098706 Valve,Crankcase Depression Regulator

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The rocker arm cover is home to the PCV valve. Start the engine and allow it to idle until normal operating temperature is reached. While leaving the hose attached, draw the valve out of the rubber grommet in the cover. Then, put your finger over the valve opening. If there's no suction, an obstructed hose, manifold port or problem with a valve could be a reason behind that. In case such hoses get blocked or deteriorated, they should be replaced. Also, turn off the engine and shake the PCV valve. If it doesn't rattle, then it is time to replace it. To do this, remove the valve remembering how it was positioned from the end of the hose. When purchasing a new PCV valve ensure you have picked up right one for your vehicle and engine size by comparing it with old one. Once you have that new valve, push it into the end of hose all way in so that it seats well. Look at rubber grommet for any damage and replace if necessary. Finally return back your PCV valve and its hose to their original place.

If you don't feel any vacuum, this could indicate a clogged hose, manifold port, or the valve itself. In this case, any plugged or deteriorated hoses should be replaced.