Suspect Posted September 20, 2009 Report Share Posted September 20, 2009 I just swapped what seemed to be a decent running L16 into my 73 Datsun. It ran rough but I figured it was a carborator issue. While messing with it, I covered the valve cover vent hole and it started to run better. I kept holding it, then something started to wistle, then that went away and I started to hear a squeel. I decided to put a vacuum tester on the hole and got over 15 cm hg vac. In other words it has enough vacuum to suck my finger and leave a blister. How is this possible? Quote Link to comment
datzenmike Posted September 20, 2009 Report Share Posted September 20, 2009 The PCV system uses intake vacuum to draw water, fuel and combustion vapors out of the crank case. Otherwise these vapors will condense when cooled and settle in the oil, diluting it and shortening the change interval. The PCV is a one way valve with a small orifice attached to the intake and a hose connected to the engine block behind and below the manifolds. The one way valve prevents a backfire from igniting any fumes inside the block. The valve cover vent allows filtered air into the motor to replace the crank case fumes drawn out by the PCV system. If you plug the valve cover vent the vacuum inside the motor will rise possibly causing air to squeeze in past the dip stick seal, valve cover gasket, oil filler cap... and make a sound. Quote Link to comment
Suspect Posted September 23, 2009 Author Report Share Posted September 23, 2009 I just removed a PCV valve from an extra intake that I had. Then I removed the one on my truck. The one from my truck had nothing in it, just an open hole. So I swaped the other one into it and it fixed the vacuum problem I was having. Thanks again datzenmike! Quote Link to comment
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