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Well, as far as I can see, you need to filter out your breather for car health reasons, and you need to re-circulate the gas coming for human health resons.

After seeing the oil in my stock "filter" foam (back when I was a newbie) I refused to connect that hose anywhere close to the intake system. So I got a K&N breather filter (it's cheap) and let the hose pollute the air through it... And ı had my custom intake system built without a breather port....
 

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Discussion Starter #3
Thats what i'm having done early next week, but was just looking at other ways instead of having to get a new K&N filter as well as a breather filter.
 

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If your talking about the hose coming from the valve cover to the intake pipe, you shouldn't be getting any oil residue from it introduced into the intake pipe. That hose is an air inlet into the crankcase so that air will flow through your crankcase and through the PCV valve, so any oil you get through it into your intake system should be introduced directly into the intake manifold. And you can install a small filter into the hose hooked to the valve cover without any worry of poluting the air, it's filtered simply to keep dust and crap from being drawn into your crankcase. However, if you are getting an oily residue into your intake pipe from the crankcase inlet tube then you may have other issues to worry about. Either your PCV system is malfunctioning or you have severe blow by indicating possibly worn rings etc.
 

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If you want an idea of what is happening.

Your pcv system is designed to use the pressure differance between the atmosphere and your intake manifold to vent your crankcase. The pcv outlet into the intake manifold is low pressure (vacuum), and the pcv inlet in the air box is high pressure (atmospheric pressure). The difference in pressure forces air to flow in through the inlet (air box) and into your crankcase, the blow by gases are sucked out of the crankcase through the outlet (intake manifold).

Even with the stock setup, the pcv system will not function well under hard acceleration. This is for two reasons, the first is that more blow by gases will be generated as you accelerate. The second is, that when you fully open the throttle, you tend to loose the vacuum in the intake manifold. But because of the air filter restriction, there will still be some flow in your pcv system, but sometimes not enough.

Now look what the air intakes you have described have done to make a bad situation even worse. In order to be compliant with pollution regulations, they have moved the pcv inlet from the airbox (whch they don't have), to the intake tube. Now when you accelerate hard and fully open the throttle, the pressure will equalize between the intake manifold and the intake tube, until you have enough rpms that the throttle body becomes a significant air restriction. So for most of the time with these intakes under hard acceleration, there is no pressure differential between the pcv inlet (intake tube) and the pcv outlet (intake manifold), and hence no air flow in your pcv system. So the blow by gases build up in your crankcase and have to vent out. The blow by gases will find the path of least resistance, which will more than likley be back out the pcv inlet.

When you don't have an airbox with your intake, the solution of replacing the stock pcv inlet with a filter on the valve cover works. This still maintains the air pressure differance between the pcv outlet (intake manifold) and the pcv inlet (the filter to the atmosphere). So your pcv system will continue to work like the stock system. The only catch is that you will no longer be compliant with pollution regulations. For pollution reasons, the inlet is supposed to placed so that any blow by gases that do backflow out of it, are sucked back into to the intake to be consumed by the engine (hence the placement in the airbox).

The reason for the filter on the pcv inlet, is to filter out dust and other large particles, so they don't get sucked into your engine.
 

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Discussion Starter #6
Its just a preventitive measure. Because with the standard airbox, there is the normal air filter, and a small foam filter (where the crankcase breather enters the box), so in a standard setup, the crankcase breather is being filtered twice, and the foam filter on all the Focus's i've been into, is always oily/greasy. But with the K&N or pipercross induction kits, there is no filtering fot the crankcase breather as the hose just connects into the back of the cone filter, and from there the air is breathed by the engine. So i'd like if possible an in-line filter, to cut the crankcase hose in half to fit in, so that there is some filtering going on before it gets drawn into the induction cone filter and through into the engine. Otherwise its a breather filter and a new cone filter next week.
 
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