2ZR Turbo Yaris

[tmontague]

Originally Posted by 06YarisRS

The open-to-atmosphere breather is there to let blow by gasses out of the crankcase when the PCV valve is closed under boost. It would also draw fresh air into the crankcase when under vacuum. At least this is my understanding of how it should work. All that said, I'm having fuel trim issues and not sure if the two are related. I'll monitor trims after I have the F/IC hooked up and the car running- hopefully. LOL.

your breather shouldn't be the cause of any vacuum issues as it is not connected to the intake in any way. How you currently have it set up is smart as the PCV is normally closed under boost pressure and any blow by will not be able to vent - therein lies the solution of the valve cover breather.

The only way I could see this being a potential issue is during idle when the PCV in barely open and pulling mild vacuum on the crankcase. The breather technically allows fresh air to enter the valve cover and potentially out the PCV and into your intake. Since the PCV venting enters downstream of the MAF (IIRC) then it is unmetered air.

Easiest way to figure this out would be to block of your valve cover breather and see if the fuel trims correct themselves. If they do than a check valve on that breather tube to stop air from going back into the valve cover should solve that issue

[06YarisRS]

Originally Posted by tmontague

your breather shouldn't be the cause of any vacuum issues as it is not connected to the intake in any way. How you currently have it set up is smart as the PCV is normally closed under boost pressure and any blow by will not be able to vent - therein lies the solution of the valve cover breather.

The only way I could see this being a potential issue is during idle when the PCV in barely open and pulling mild vacuum on the crankcase. The breather technically allows fresh air to enter the valve cover and potentially out the PCV and into your intake. Since the PCV venting enters downstream of the MAF (IIRC) then it is unmetered air.

Easiest way to figure this out would be to block of your valve cover breather and see if the fuel trims correct themselves. If they do than a check valve on that breather tube to stop air from going back into the valve cover should solve that issue

You, sir, are a wonder! I was thinking about doing precisely what you mentioned with regard to blocking the breather hose and checking fuel trims. I hadn't thought about the check valve but may have eventually come to the conclusion to try the valve. So, you wouldn't anticipate any issues with, say, an extended period of idling and no way for fresh air to get back into the crankcase as it would stopped by the check valve. I guess I'm not sure I fully understand this system as the original valve cover vent was connected to the intake pipe before the MAF sensor, which, I assume, would also have vacuum on it. How would fresh air ever enter the engine if both the valve cover vent and PCV are under vacuum? Help me understand. LOL!

I am going to check my vacuum again this evening, but even with the open valve cover breather, I think I was getting around 25"/hg at idle. I'll monitor vacuum with the valve cover breather blocked off and not blocked off. BTW, I did test my oil catch can and it's sealed. When I started opening the ball valve, I could hear strong suction and the engine started to stumble. Close the check valve and idle went back to being smooth.

[tmontague]

Originally Posted by 06YarisRS

You, sir, are a wonder! I was thinking about doing precisely what you mentioned with regard to blocking the breather hose and checking fuel trims. I hadn't thought about the check valve but may have eventually come to the conclusion to try the valve. So, you wouldn't anticipate any issues with, say, an extended period of idling and no way for fresh air to get back into the crankcase as it would stopped by the check valve. I guess I'm not sure I fully understand this system as the original valve cover vent was connected to the intake pipe before the MAF sensor, which, I assume, would also have vacuum on it. How would fresh air ever enter the engine if both the valve cover vent and PCV are under vacuum? Help me understand. LOL!

I am going to check my vacuum again this evening, but even with the open valve cover breather, I think I was getting around 25"/hg at idle. I'll monitor vacuum with the valve cover breather blocked off and not blocked off. BTW, I did test my oil catch can and it's sealed. When I started opening the ball valve, I could hear strong suction and the engine started to stumble. Close the check valve and idle went back to being smooth.

25mm/Hg in a good vacuum value during idle- I think I used to see 25-27 give or take on both my 1nz and 2zr back when I had a vacuum gauge set up. Have you checked what happens to your FT's when you hold 3k rpm?

I just checked my engine bay and what I thought earlier was correct: there is no vacuum hose that connects upstream (before) the MAF sensor and the only hose that connects before the TB is the valve cover vent. Because this hose is located prior to the TB, there is never really any vacuum on it. It would only really be able to "suck" air in during moderate to heavy throttle and even then, vacuum is very little at that point so it is more of a passive vent that happens to vent into the intake as opposed to an actual vacuum pulling air out of the valve cover.

Vacuum can only be had post TB as the TB restriction is what creates the vacuum with the help of the engine sucking air in. Think of a vacuum cleaner with a 5' diameter hose. You wouldn't ever really create a vacuum to suck dirt up. But with a 5" diameter hose or even less, you can suck dirt up.

I'm not sure why you think the crankcase needs to have fresh air go into it, it never really ever does. The crankcase never needs fresh air, it simply needs to vent excess pressure above ambient when blow by happens (it always happens, just at varying degrees). WOT and turbo motors create more blow by hence why people recommend turbo builds to have catch cans and/or breather set ups.

The 1nz and 1zz is much different than the 2zr in the way the PCV is set up. In the former engines, the PCV is located on the valve cover and it is the sole vent port for the crankcase (crankcase gases travel up into the head). This makes it easy to attach a catch can.

On the 2zr, the PCV is actually located under the intake manifold as you know, but it is attached to the engine block and separate from the head. Therefore there is also a breather tube on the head that runs into the intake before the TB - this is where you current breather it hooked up to. I am assuming Toyota did this as the head needs to be vented just in case of a situation where pressure builds up there (the highest location of the engine) since the PCV is much lower on the block.

Your PCV is taken care of with your catch can and your head is vented via your breather set up. None of this should cause a problem theoretically as the head should never have a vacuum in any situation and pull air in from your breather. That said, definitely clamp off the breather and see what happens to your FT's. Once that is done, rev your engine to 3k rpm and see what happens to your FT's.

Your engine doesn't need air going into it as it will never be in vacuum, the only thing it needs to do is be able to expel excess pressure from blow by out so as to not blow any seals. Years ago this was just vented to atmosphere as you have done with the breather. Ever since tightening emissions standards the PCV system has come to be the norm.

The PCV valve itself is virtually closed during idle and in any excess pressure situation (boost). It is fully open during WOT where there is little to no vacuum seen on it. In a boosted cars case, any time you are WOT you are usually in boost and therefore not venting the PCV. This is why a breather hose is typically a good idea.