After seeing a decent sized oil leak in my garage after beating on the truck a little bit, I figured out that the PCV setup that I had built was not working very well. I hooked a pressure gauge up to the dipstick tube and saw that I was building about 3 psi in the crankcase under boost. I added a breather to the driver's side valve cover, and that fixed the problem. No more pressure buildup, no more oil on the garage floor.

But....I seem to run almost a full point leaner than I was before. I had my tune dialed in for 11.5 in Sacramento, and when I came back to Phoenix it was rich, in the high 10's. Now that I have relieved the crankcase pressure, it seems to have leaned out to about 12:1. Is this normal? Is there some way that relieving the crankcase pressure would cause a more complete combustion, causing the wideband to read leaner? I also noticed that without touching my boost controller I seem to have lost about 1 or 1.5 psi of boost. Could this be related as well?

 

Did you feel an increase in power? Your engine was working against the pressure in the crankcase so you should be seeing more power now, more power = leaner

The loss of boost seems strange since you have a turbo and it's speed is not fixed by a belt/pulley but, can vary to reach the wastegate setting. Where is your wastegate reference hooked up?

 

Could it be that when the crankcase was pressurized you were getting cylinder intrusion (reverse ring blow-by) that was reducing the amount of fresh charge air that was entering the cylinder on the intake stroke and aiding in evacuating the cylinder at the start of the compression stroke (dependent of camshaft intake lobe timing if close occurs after bottom dead center)?

Now you are getting more fresh air into the combustion chamber which is allowing for a more complete burn, using up more of the fuel you are commanding.

 

Kinda like an EGR through the rings.

 

I think you have a point here, combine your thinking of working against the pressure in the crankcase to the thought process of load on a turbo. Increased crankcase pressure would increase the load on the engine as it has to do more work per combustion event. Combine that with the possible theory in my first post and I can see how reducing the crankcase pressure effectively reduced the boost pressure. Not loosing power, just manifold pressure.

 

Yeah, I thought about it possibly being just the manifold pressure reading being lower now due to less load but, what confuses me is that the turbo should hold whatever boost the wastegate is set for.

On a blower setup with a fixed pulley size I could definitely see what you are talking about happening.

 

Good insights guys, I was thinking something along the same lines...having trouble putting the abstract thoughts into a reasonable explanation though.

 

Is it leaner everywhere in boost or only once you've reached peak boost?
If you've dropped 1-1.5 psi you're not in the same part of the map as before and maybe your map is just leaner there.
Temps are cooling off too = denser air = leaner mixture.

How did your plugs look before the pcv change? If you had a pressurized crankcase you might have been blowing some oil past the rings, resulting in what looked like a richer mixture...now less oil = leaner mixture.

Just throwing some ideas out there...

 

The plugs were fine last time I pulled them, but that was before I started beating on it. Haven't checked them since. I had the truck tuned for lower boost, so if the boost has fallen off it should still be ok.

 

Remember, Sac is sea level, Phoenix is 1200+ feet and hotter. Your at less air pressure, so your going to see a little less boost and remember how much you leaned out when you came up here?