Originally posted by Nashty
That's true, when the engine isn't running. But when the air starts moving, things change. The inlet bell is pulling air into it, air doesn't just wander in there. That is a vacuum source. If you need me to explain that I can. The PVC is also a vacuum source. The air being pulled in isn't referenced to atmospheric unless you open it up with a breather.
My whole point is that this will affect the calibration of the whole system. You talk about the importance of the calibration being correct for it to work effectively. That's what I'm trying to say. But ANY changes will affect it's flow rate to some degree.
Even if it is referenced to atmosphere, there is still a pressure differential or else no air would move at all. It doesn't matter if there is a vent to atmosphere from the factory or not, you are changing the size of that and thus, changing pressure the PVC will effectively see.
Am I being condescending? I'm trying not to be. It seems every damn post I get back is speaking down to me. No wonder people get so pissy on this board. Need I repeat that?
Even I'm getting confused now
I look at it this way. The PCV is connected directly to the top of the throttle body. This, during idle for example is a source of pretty strong vacuum (19 InHg on my car), and is pulling this vacuum through the crank case. But since the passenger side valve cover has a vent (tied to the turbo inlet) which is for all intents and purposes at atmospheric pressure (still at idle) because if you were able to look through that tube and take a sharp left when entering the turbo inlet, you'd find your self at the air cleaner. So the air in the inlet (some small portion) is being drawn in through the valve cover, and ends up being pulled through the PCV and dumped in behind the throttle plate.
The other extreme is under heavy boost, the PCV should, realistically stop any pressure at the throttle body from going through the PCV into the crank case.
But as we all know there is some leakage there. So some small portion of the boost pressure (OK medium portion) enters the crank case. Now it has to find a way out by taking the path of least resistance (sort of like electricity), this path is out through the passenger side vent, which just happens to be tied to the turbo inlet. These vapors are how oil ends up in the turbo and intercooler. The vapors are coming out of the crankcase and can be heavilly ladened with oil particulates.
Here's where the problem of the check valve that ATR markets comes into play if you use it to completely replace the PCV. And this is easilly demostrated if you have a check valve in hand, and an 893 PCV. First (if this is a new 893 PCV) blow into the top of the PCV as hard as you can. Some blow by, yes, but not a lot. PCV's that are about a year old will allow considerabley more.
Now blow into the top of the check valve as hard as you can. No blow by. This so far, is a good thing.
Now take a suction on the top of the PCV, and inhale as hard as you can (new PCV!), you will notice some restriciton to the flow (this is the calibration we talk about).
Do the same thing to the check valve. There is absolutely no restiction to the air you're inhaling!! To much of a vacuum leak!
This, for some reason really manifests its self in the Thrasher chips (not all of them), and other brands as well, but not all, and I don't pretend to understand why. But when I was using the check valve and finally got day-to-day scan tool hooked up, the most glaring thing I saw was my O2 drop to neary zero at idle (no I'm not talking about DE or DFCO). Idle was smooth enough, just funky O2's.
Removed the check valve and installed a good PCV, and all was well again.
AT certain vacuum levels (highest) is when this problem occurs the worst. There is much more air entering the engine than the normal 5 grams that the MAF is seeing, and plays tricks on the PCM.
