Tube From Valve Cover - What Is This And What Does It Do?

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The passenger side valve cover on my 98 Expedition 5.4 has the PCV valve. The driver's side valve cover has a soft elbow with hard tube that goes into the throttle body plenum.
Here is a picture.
[Linked Image]


What is the function of this?
When I removed my intake plenum, there was oil in it. I replaced my passenger side PCV valve, since that was presented as a potential problem, but now that I see this. Is this another PCV valve? Is this another potential place where oil could enter the intake system?
When I removed the hose, it had oil on the outside of this piece.
[Linked Image]
 
It admits clean air to the engine in that valve cover,> This air sweeps thru the engine picking up water vapor, blowby etc. Then is sucked out the other valve cover thru the PVC valve and burned.
 
This is the fundamental PCV system that has been on every car since the 1970's. Filtered air goes into the crankcase through that tube. The air then leaves though the other valve cover and the PCV valve. Much of the oily crankcase vent gas that was simply released to the atmosphere in older cars gets burned up in the engine.

If the rings are worn and there is a lot of blowby gas, or if the PCV valve is clogged, the flow through that tube can reverse and send smoky air and oil into the intake pipe before the throttle body. There is a baffle inside the valve cover to try to reduce the amount of oil that comes out that way.
 
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Fresh air line.

Anything going out the PCV valve has to be replaced or a vacuum would form inside the engine crankcase. The replacement air, fresh air, flows in thru that line to replace the blow by gases exiting thru PCV.

On some engines, the direction of flow in this line will actually reverse when the engine is operating at maximum torque output, and this can lead to some oil getting onto the air filter at the spot where the tube connects to the air box.
 
Thanks for the input. Is this a valved part that should be changed like the PCV valve on the passenger side?
 
Nope, it's a simple tube. You just want it intact, so that it's bringing in filtered air vs gritty air.

Fun fact, you could put a "breather filter" on it and it would work great, but dribble an oily mess down your valve cover, onto the exhaust and street.
 
Originally Posted by Fitz98
Thanks for the input. Is this a valved part that should be changed like the PCV valve on the passenger side?


No, only when one of those boots on either end gets spongy or the tube cracks.
 
Originally Posted by bdcardinal
Originally Posted by Fitz98
Thanks for the input. Is this a valved part that should be changed like the PCV valve on the passenger side?


No, only when one of those boots on either end gets spongy or the tube cracks.

BD, Is the boot an independent replaceable part? Mine looks like it could use replacing, but the tube is still in great shape.
 
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