The PCV is a one way valve, you should be able to blow into the hose end only. They do definitely go bad from getting all gunked up inside. They're so cheap they should be changed about once a year anyway.
PCV valve=positive crankcase ventilator and does just that. Ventilates vapors from the crankcase. Remember the cars from the 60's that ya always seen the 3/4" tube sticking down to the bottom of the engine and would bellow smoke when they were all gunked up? This replaced that crakcase pressure relief. If gunked to the point of not working (actually is a check valve) rough idle will happen as this works on your vacuum system. If it does not rattle it can be cleaned with injector spray. Blow in the engine side of the valve, should let air thru. Suck on the engine side of the valve and it should block off tight. Not an expensive item but also rarely fails just needs cleaned from time to time.
Typically a PCV valve fails by getting enough crud in it to prevent it from operating.
You can check it by removing it from the valve cover and shaking it. If it rattles, then it's OK. Take the time to give it a visual inspection. They are usually very trouble free components.
Oil Can Henry's and the like will try to sell you one of these and an air filter about every time you change oil. Engines run so clean now the PCV valve seems to last forever. If it rattles when shaken as this poster says and with the engine running, remove it from the valve cover and it pulls a good vacuum, as another poster says, its works. That's all it does. I replace mine once every million years, or when the vacuum hose and grommet that the PCV valve attaches to rots away, which ever comes first. Then it's a 'while I'm there' type replacement, not because it's shot. Don't think I've actually seen a gunked up PCV valve since the 70's, and that would have been on 60's cars. Even then it's most likely an indication that the rings and/or valves are shot.
PCV= Positive Crankcase Ventilation. Pretty self explainitory. Crankcase gasses used to be vented to the atomosphere through a draft tube. Since the late 50's or so, these gasses are vented internally through the PCV system.
A symptom of a non functioning PCV valve would be oil accumulation at where ever the breather for the PCV system is, typically in the air cleaner housing. On a carborated vehicles, the idle mixture will be rich.
Last edited by newbecorvetteguy; 07-21-2007 at 01:02 PM.
My new one (probably chinese) didn't fit tight in the hole, so I put some High Temp silcone aroung the diameter of it and let it set, then slid it in the next day and fit nice and snug. Just a suggestion.