The blowby that was pressurizing your crankcase, that is now going into the atmosphere instead of your intake, is not air, it is blowby past the rings. Because it is blowby, it has the same A/F ratio as what is in the cylinders. Putting it back into the intake is the same as having a mini carburetor adding a 10.5:1 (or whatever) mixture upstream of the injectors. Now you are letting it out into the atmosphere instead of burning it.
Not that you care about polluting the air, but that is the reason that the manufacturers go through the trouble of installing PCV systems.

 

I am aware of that. I'm not talking about a difference between Sac and Phoenix. I'm talking about a difference between Phoenix and Phoenix, within one day of each other. Altitude and temperature should play absolutely no role in this situation.

It was not returning to the intake manifold before either. Both ways it was set to vent to atmosphere, this one is just more efficient, lol.

 

Even 11.5 is a little lean for a boosted engine. You should be in the 10's.

 

Maybe what changed is the vacumn, it's pulling through the breather on the can and it has the same effect as pulling a vacumn line off.........................just a thought!

 

Even so, don't you think my answer was pretty good?

 

I agree that it is blowby past the rings. But the pressure would build in the crankcase and then make its way through the oil passages. This is oil not air and fuel anymore. If the pressure is relieved better there is less resistance when the pistons travel downward (think a slight reverse compression stroke). This would lead to a faster revving requiring more fuel. I think that is what is happening.

 

I was joking, and I am pretty sure that you spelled your name wrong, unless you meant for it to rhyme with "raped". It wouldn't be the first time I was wrong in this thread, though.

 

I had the same thing happen with my truck when my STS PCV check valve went bad. It was pressurizing the crank case and eventually blew my PCV line off of the valve cover and it started running stronger and leaning out. I put a new pcv setup on with a catch can and breathers and I could tell a noticable difference in power and my af was leaner. I can't remember if it messed with my boost level but I did have to do a retune.