The PCV valve on a 1997 Nissan Hardbody 4-cylinder is located on the
valve cover. It's a small, usually plastic, valve that's often capped with a hose. It's not always easy to spot, so you might need to carefully inspect the valve cover itself. Look for a small, usually cylindrical, component with a hose connected to it, possibly near the spark plug wires or other hoses connected to the valve cover.
A diagram of your specific engine (you'll need the engine code, often found on a sticker on the engine or in your owner's manual) would be helpful for pinpointing its exact location. A repair manual specific to your year and engine will be the most accurate resource.
