I don't know where to put this question in the forums, so I hope this is a good spot. I'm curious about exactly how the PCV system on the 80's Fords work. I'm assuming that the PCV valve pulls on the crankcase to relieve pressure from one side of the engine, while the breather filter going into the other side allows fresh air to circulate back into the crankcase. This is according to my Haynes manual. If this is the case, what does it indicate if the crankcase is ventilating OUT through the PCV AND the breather filter?

 

Redwood,

The PCV system (positive crankcase ventilation) uses manifold vacuum to pull pressure and fumes from the crankcase. In order to do this it must be able to pull air from someplace (can’t pull air through a straw if you have your finger over the other end) and that is the oil filler cap which has an air filter attached in order to make sure you are not pulling dirt through the motor.

The inside of the motor is rather open and thus there are not two sides, but rather one area with two peaks (each valve cover). By pulling from one cover and supplying the air through the other cover then you are assuring that there is complete ventilation of the crankcase.

The purpose of the PCV system is to reduce the pressure created by the natural blow from the piston rings during the combustion process. If the crankcase is not properly ventilated either from a non-functioning PCV or excessive pressure from bad rings then the pressure can force oil out of the oil pan and through oil seals.

I hope that helps clear it up in your mind.

Good luck,

Mark

 

On the valve side...flow is always from PCV valve to intake (or carb base)... the 'fresh air side" reverses flow when load (and blow-by) is high and vacuum is low. The "fresh air side" should go to the air cleaner... not a breather cap. If you have flow to the induction on both hoses this indicates excessive blow-by and/or bad PCV valve and/or low vacuum (insufficient scavenging).