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
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 vacuum 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 to prevent block pressurisation , but helped by the little reed vavles situated inside the intake manifold runner gasket.
Now the WOT/High
positive pressure side
Under wide open throttle the vacuum 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
and to make sure no pressure gets past them and pushes on the diaphragm and all is well.
In turn there is still alot of vapor pressure and positive pressure 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 throat of the turbo which under boost will suck on this valve, which is connected
via the lower manifold to the cylinder block, oil vapour pressure gets pulled into the high pressure air stream and pushed through the intercooler and piping and the burnt inside the combustion chamber
Thats where the oil filter housing 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......
we started looking at the low pressure / vacuum side
For some reason oil mist must be suck or blown into the combustion chamber.
Secondly the pressure in
the block tries its best to escape.
We tried venting the pressure side . Which didnt help as the car would suck in un measured air and would run lean under high vacuum low throttle..........................................
To be continued