There is a very simple way to check the entire pcv system. This system is designed to maintain a flow of fresh air through the crankcase/valve cover system. It does this by using manifold vacuum to draw a calculated amount of air from the air cleaner through the engine internal spaces and into the engine to be burned. Since most of what needs to be ventilated is blowby past the pistons and is largely unburned fuel, this reduces polution. Pcv replaced the antiquated road draft tube system somewhere around 1962. A good pcv system really keeps the inside of the engine clean. It is the original "smog device".

Anyway the test is simply to have the engine warmed up and idling. Remove the oil filler cap and apply a piece of paper larger than the opening to the opening. If the engine is healthy, and pcv is operating properly, the paper will be lightly but positively sucked onto the filler opening and will be retained there. A corollary to this is that you should not see oily vapors flowing out of the filler tube.

Is this test perfect? No. A worn out engine with lots of blowby will swamp the system and the paper will not be retained. But in a reasonably healthy engine, this test has worked well and served me well for many years.

My box of rox sounding 91 4.0 with 186000 miles still passes this test, go figure.

Ken