The Volvo/ FORD ST pcv system is made out of two parts like most cars.
There is high vacuum /low throttle side, and then wide open side ,Low vacuum
high positive pressure side and its a complete closed system.
Now lets look at the high vacuum side
During this state oil vapor inside
the engine is sucked into the intake manifold through the oil filter housing which is open to the bottom of the cylinder block and connected to the cam cover.
Inside the OFH you will find a diaphragm which regulates the flow as the vacume pull is rather
strong, strong enough to suck in the oil seals on the cams and the crank , causing them to leak.
This particular diaphragm also act as a shutof valve when the car is in boost, but helped by the little reed vavles situated inside the manifold runner
Now the WOT/High positive pressure side
open throttle the vacume in the intake manifold turns to positive pressure. Now the little reed valves gets blown againt their seats to close the system from the pressure to make sure no pressure gets past them and pushes on the diaphragm, and all is well.
In turn there is still alot of positive vapor pressure and inside the block that must go somewhere,
this is where the secondary system kicks in
Volvo utilizes an anti pollution regulating valve at the turbo, now this is connected at the throught of
the turbo which under boost will suck on this valve which is connected via the lower manifold to the cylinder block, oil vapour gets pulled into the high pressure air stream pushed through the intercooler and piping and the burnt inside the combustion chamber
And all is well!
Thats where the problem stems off.
So in the past we focussed on the Boost / high pressure side
Some boost leaked past the reed valves, causing pressure on the Diaphragm located in the OFH, causing it to rupture.
End result was usually a high pitch scream at idle.
Our fix at the time was a swing action one way valve with an enclosed catch can.
It worked, saving numerous diaphragms in its stride
then we found more and more Tuned cars with a smoking habit!
Now where do we start......
So we started looking at the low pressure / vacuum side
some reason oil mist must be suck or blown into the combustion chamber.
We tried venting the pressure side . Which didnt help as the car would suck in un measured air and would run
lean under vacuum............................................
Now we found that intecepting the hose from the rocker cover works.
directing the gasses to a vented can and then back to the OFH.
This way pressure vents via a pod filter and any leftover oil is directed back to the ofh.
This help the OFH last longer and none of the oily mess associated with it