I posted this question in the FI forum and bumped it 4 times and noone wants to repsond. Maybe i'll have better luck in the tech forum...

Whats everyones opinion on hooking up an oil catch can. Obvoiusly the best way to do it would be to pull off the whole EVAP canister and hook up the catch can to the port on the back of the block, but how good would it be to hook up the catch can to the line that runs back to the IM? Hopefully my post made sense. To clarify, the only reason for this would be just to make the install easier.

and a OT side post: Doesn't a turbo turbine cool down the exhaust (for the same reason a compresor heats it up)? If so, wouldn't your O2 sensor always read rich?

TIA

 

A catch can would be for the PCV system. That's got nothing to do with the EVAP system, so I don't get what you're saying about the line from the EVAP canister??

People say a turbine 'cools' the exhaust, but that only makes sense when you make the following comparison... If you had a compressor on the intake (say a supercharger), so the combustion temperature & pressure were the same as they are in your turbo... Then the exhaust comes straight out without going thru a turbine... Your exhaust (with a turbine) is cooler than THAT example.

But either way, once the O2 sensor comes up to some threshold temperature, it's measuring oxygen content of the exhaust. If it was reading temperature then it'd be called an 'exhaust temperature sensor'.

 

Thanks a ton JimBlake! I misunderstood and thought that a 02 sensor measured the oxygen content based on the heat of the exhaust and a wideband measured the oxygen content itself.

As for my main question. I thought the EVAP canister is what crankcase fumes flowed to from the back of the block. I know when installing an oil catch can replacing the PCV valve on the valve cover only gets a small portion of the oil as compared to wherever the fumes flows out of the back of the block. Doesn't this line return to the IM somewhere? (I doubt it goes to the atmosphere) Let me know if i'm confused about something.

 

I think widebands are better O2 sensors that can measure over a wider range of oxygen levels.

The EVAP canister is the charcoal canister that takes evaporated gasoline from the gas tank. The breather box on the back of the block is like a catch can, only a bigger catch can works better, catches more of the oil.

On my B-engine, the PCV valve is on that breather box, not on the valve cover. That hose on the valve cover is the breather.

 

Okay, cool. Thanks again. Your right that is just a breather hose on top of my valve cover. So anyway, my question is where does that breather box return to the intake (or does it). There is some vaccum source on the middle of my intake manifold body, but i'm not sure what it is for. Is this where the breather box returns fumes back to the intake? If it is, can you just connect that hose to your oil catch can? Thanks a ton JimBlake!

 

Since your engine's boosted (right?), I don't know all the answers...

Un-boosted, here's how it's supposed to work. Vacuum hose from intake manifold is connected to the PCV valve which is on the top of the breather box. This sucks oily air out of the crankcase, but the breather box is supposed to let the oil drain back into the crankcase. So the breather box is kinda trying to act like a catch can. Some engines have the PCV valve on the valve cover - then there's baffles built into the valve cover to act like that breather box. Either way, that hose goes to the intake manifold.

The breather tube at the valve cover is to bring fresh air from the intake, to make up for what is sucked out by the PCV valve. At WOT, there's not much vacuum sucking air out, so the blowby can overwhelm the PCV valve, & crankcase vapor blows backwards thru the breather, getting sucked thru the throttle body & burned.

Under boost, you don't want to pressurize the crankcase. So the PCV valve acts like a check valve, & it doesn't let air flow 'backwards'. For the same reason, I think you want to connect your breather hose (from the valve cover) UPSTREAM of the compressor.

You can put a catch can in the valve cover breather line, for the times when it's flowing backwards. Especially if you spend a lot of time at WOT... You can put a catch can in the PCV hose, to catch any oil that gets thru the breather box & PCV valve.

 

awesome. I'm going to disconnect that vaccum line that runs to the middle of the intake manifold and hook it up to my catch can, assuming that it runs to the breather box/PCV valve and have it vent to the atmosphere. That way no matter which direction the air flows it will go through the oil catch can.

I'm still confused why everyone pulls out their breather box and messes with freeze plugs and fittings and all that when installing an oil catch can. Why don't they just hook the vapor fumes return line that returns to the intake manifold straight into their oil catch can?

 

No, you need the vacuum to pull air out of the crankcase. If you put a catch can in the PCV line, then the other line on the can goes to the manifold like before. The lines still go where they're supposed to, but the catch can traps more of the oil.

 

Yeah, but a lot of FI applications vent to the atmosphere since there isn't a vaccume source anywhere (unless u have a piping before your turbo). I think the postitive pressure of the crankcase would be enough to keep the crankcase ventalated.

 

Your intake manifold is frequently at vacuum. During normal driving anyway...

I guess I'm mostly talking about a factory setup that has to be street-legal. Manufacturers have to keep the EPA happy. Like Saab's factory turbos. Yes, the breather comes from upstream of the compressor. And the PCV tube goes to the manifold, because you still have vacuum a lot of the time. Only when you're in boost does the PCV valve close; then any blowby goes into the intake, upstream of the compressor.