The PCV valve is a pretty simple device, but it performs a potentially critical function.
It is, essentially, a regulated vacuum leak, drawing contaminated air from the crank case, rather than letting it vent to atmosphere, as in days gone by.
If you look at old pictures of roads and highways, you will notice a dark stripe in the middle of each travel lane. That's mostly from crank case oil vapors condensing in the breather tube, then dripping onto the road. It was called a "road draft tube" because it hung down enough to create a small vacuum as the vehicle moved through the air.
Air was draw into the crank case through a filtered oil filler cap on most vehicles back then.
Since the 1960's, the crank case gasses have been pulled into the intake system, to be burned with the fuel/air mixture.
Here is a picture of the PCV valve used on the Jeep JK.
It's about 1 3/4" tall.
This is a picture of what's inside the valve. Crank case vapors are draw into the hole in the bottom, pass by the tapered cone, out the top, and through the hose connected to the intake.
In the picture, the valve is in the low vacuum, high load position. It is open to allow the most flow, because under load, the intake is producing the least vacuum, but the engine is producing the most blow-by into the crank case.
In this view, valve is in the high vacuum, low load position. The tapered cone is drawn up, into the exit hole, to restrict flow, because the engine is producing less blow-by vapor. It also decreases what the engine would see as a vacuum leak.
Oil is continually being thrown around inside the crank case, producing an oil mist saturated atmosphere. If the PCV valve were to remain fully open during times of low load/high vacuum, this oil mist would be drawn out, too. An increase in oil consumption may be observed, along with a rough idle because of the vacuum leak.
This view shows the air hoses for the PCV system. A hose is connected from the intake to the PCV valve. As air is drawn out, it is replaced with filtered air from the intake box. Clean air is constantly flowing through the crank case.
Pictured is the location of the PCV valve. It is tucked away behind the coil pack.
This is how I easily removed and installed the PCV valve:
Removing the coil pack is easy to do, and greatly improves access to the PCV valve.
It may not be necessary to pull the plug wires from the coil pack, as it may drop completely out of the way.
If it doesn't drop out of the way....
Disconnect all six plug wires at the coil pack. The stock wires and the coil pack terminals are numbered, so no need to worry about marking them.
Remove the two bolts marked with yellow arrows.
Leave the main electrical plug, marked with red arrow, connected.
Rotate the coil pack up and out of the way. It will tuck in behind some of the wires, and stay there.
Now that you have plenty of room to work, remove the clamp from the PCV hose. Pliers will do it, but a hose clamp tool designed for this type of clamp will make it easier.
You now can see the PCV valve recessed into the adapter.
Put a zip tie on the neck, as pictured. Make sure it's a good, strong zip tie, and is tight around the neck.
Grab the zip tie with some pliers. Rest the nose of the pliers on the intake manifold, as in the picture.
Pry up with the pliers. The valve comes out so fast and easy, it actually may make a "pop".
Place the new valve in the adapter. It will be hard to push home, so get a socket just big enough to fit in the adapter. The socket wall should be thick enough so it will push the valve, and the rubber seal.
An extension on top, long enough to stick above neighboring lines, will allow you to push or tap the valve home.
Here is a pic of the valve after seating it with the socket.
Reconnect the hose with the clamp, to the PCV adapter.
Reinstall the coil pack, connect the wires to the appropriate terminals.
When you push the plug wires onto the terminals, make sure you hear them snap into place.
Remove all tools from the engine bay.