January '19

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52 THE SHOP JANUARY 2019 52 THE SHOP JANUARY 2019 low manifold vacuum at idle, such as an engine with a hot cam and a tight torque convertor where the PCV valve is pulsing from the open to closed position at idle creating idle quality problems, a fixed-orifice PCV valve such as part #V372 from Standard Motor Products will often cure the problem. The fixed-orifice option also works well with a computer-controlled fuel- injected engine because it is easier for the computer to trim the air/fuel mixture for a fixed-vacuum restriction than it is with a continually changing or pulsing PCV valve. VACUUM SOURCE FOR THE PCV VALVE The vacuum source for the PCV valve should connect to a place on the engine's intake system that will allow the crank- case vapors to equally distribute to all the cylinders of the engine. The most common vacuum source most engines use is a 3/8-inch vacuum tube located on the baseplate of the engine's carburetor. Note: Some of the newer aftermarket carburetors have a 3/8-inch vacuum tube under the primary fuel bowl that is intended for the PCV vacuum but is necked down to 1/4-inch as it enters the baseplate. In my opinion, this may not supply enough flow for the PCV valve to operate properly. If you are connecting the PCV valve to the intake manifold, it's best to con- nect it to the intake manifold plenum. If the PCV valve is connected to a port on the runner that goes to one or two cylinders, it may cause those cylinders to not have the same air/fuel mixture as the other cylinders. VALVE COVERS & OIL CONSUMPTION The PCV valve should always be located in an area that allows it to remove vapors from the crankcase without exposing it to liquid oil or oil spray. The most common location for a PCV valve is in the valve cover of a V-8 engine, but there is a lot of engine oil floating around in the valve cover that is being thrown off of the rocker arms. Ford, General Motors and Chrysler used baffles or oil separators to shield the PCV valve from direct exposure to engine oil. Some aftermarket valve covers have This 3/8-inch hose nipple on the base of a Holley carburetor is a good source of vacuum for a PCV valve. This necked-down vacuum nipple on the base of the carburetor is not a good vacuum source for a PCV valve because it may not flow enough air for the PCV valve to operate properly. Positive Reinforcement

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