Hello again folks! I have a rather puzzling issue going on here with my '81 F100 300/6. I've had this noise I thought was a vacuum leak from under the dash or engine compartment, or worse yet, some type of bearing going out. A couple weekends ago, I was investigating and I saw a cracked vacuum hose leading from the PCV valve to the carb/manifold area. The top hole in the PCV valve had already been plugged by my mechanic. I decided to change the vacuum hose and PCV valve, and I plugged the top PCV hole like the old valve was. Now the noise is laouder. I finally tracked it down today and it's the new PCV valve, which is buzzing/rattling loudly, even when I pull the valve out of the valve cover. Anyone out there hear of this happening, and does it mean anything?

 

Sounds like something is hooked up wrong. The PCV vents the engine to the intake (basically). Take a piece of paper napkin and lay a corner of it over the hole in the valve cover and do the same thing to the PCV after it is out of the valve cover but the vacuum hoses are still connected. All of this is while the motor is running. While the paper is over the vent on the valve cover, it should be blowing up gently, more as you rev the motor. The PCV should hold the paper to it with mild suction, more as you rev it up. You should also get a vacuum diagram and check all the hose routings.