I've been re-assembling my motor and the old owner gutted most of the emissions equipment in the car. Since I've had to piece together almost every missing piece, I thought I would write up what every part does and why it's missing. This car failed emissions testing almost all the time, and during the rebuild, I now understood why.

Today's topic, the PCV Valve.

Some people remove it, or put a filter on it or use a road draft tube, but if you ever worked on a motor with a lot of sludge and varnish, it's probably because of a failed or non-working PCV Valve.

In the old days, there used to be a road draft tube and the manufacturers would direct the blow by gases to the road. At idle, you could smell the fumes escape from the oil filler cap. The vacuum from driving would vent the crankcase of blow by gases which consist of unburnt fuel and oil. This method still caused sludge and varnish in the motor.

For the people on the board that are thinking about removing the PCV valve, keep this in mind:

Without the PCV Valve you can get:

-more sludge and varnish in the motor (Think of the times you've ever worked on a motor with oil caked on the lifter valley and in the heads. The cause is usually a failed PCV Valve.)
-Failing gasket and seals due to the PCV valve being stuck closed or not being there to vent and the pressure building up
-If the PCV valve is stuck open, you can get rough idling and if you have a carburetor you can get oil soaking of the air filter element.
-The PCV valve reduces Hydrocarbons by 20% without robbing horsepower. (It's just s bunch of hoses from the valve covers to the intake and it's not run by a belt. The gases just move from the valve covers back into the intake to be re-burned.)

 

Not to mention that you can literally blow your oil pan off if you get a buildup of fuel vapor in the crankcase. Run the PCV. It's the first and most useful of the emission devices. Plus engines are designed to run with this large vacuum leak. You can't just plug the PCV port on the carb.