[gde061]

I am hoping someone can explain to me what may have been done to my 335xi by the prior owners when they put on some mods. The car is a 2008, and it was upgraded with a VSRF intake and catless downpipes, among other things. There was a spent oil mess all around around the bottom of the engine and I though it was the oil pan gasket, but it is at my local import mechanic now and he said there is a hose coming off the back of the engine that should be connected to the intake, but in my car it was just run up to fresh air and not connected to anything.

From what I can infer, this might be the flapper valve tube from the PCV, which was just left to drain to the atmosphere. I do not believe it has an oil catch can, but it's possible at some point it had one and it was removed, or a catch can install was attempted and abandoned...

Basically this particular mechanic is a "stock" BMW guy, and he gave me his opinion that I should go back to the stock intake. That's not what I had in mind when I brought the car in. I would much rather add a catch can or do something else to properly modify my setup. I'm at a loss to think what else it could be besides the PCV tube ... but I suppose it could be something else... ** edit --- I've added a picture below **.

Both intake hoses have a plugged port that I'm thinking might be where this is supposed to run back to, assuming it's the PCV tube. I've marked on of the ports that is visible in the pic in red...

I'm wondering what this sounds like to others here, and whether this kind of setup in something that anyone has seen (or done) on a car with the VSRF intake.... maybe as a way to keep the emissions light from going on... ?

Thanks for the help.

[gde061]

Just want to add... I found a discussion of this here: https://www.n54tech.com/forums/showthread.php?t=39960

Looks like a VTA setup or VTA catch can configuration is not unusual. Some of the discussion was over my head... I don't know if the prior owner deleted the flapper or not, as well as what is meant by "vacuum-side PCV system".... maybe someone here can explain? Thanks.

[arkie6]

The N54 engine in your car has two modes of PCV operation; 1) engine under low load / intake is at a negative pressure (vacuum), and 2) engine under moderate to high load / intake is at a positive pressure (boost).

In mode 1 (negative pressure), six small ports in the head directly in front of each cylinders' intake valves pulls crankcase gases (and oil vapor) through the PCV valve mounted inside the valve cover. Air flow for this pathway is from clean side of air filter > rear turbo inlet pipe > PCV heating element > 3/4" accordion hose > PCV flapper valve bypass hole > intake valve cover > PCV valve > 6 intake ports. A key point to note here is that the air flow into the PCV system is filtered. If you just have that flapper valve fitting dangling out in free air with no filter on it, dirty air is being drawn into your engine via this path.

In mode 2 (positive pressure), turbo boost pressurizes the intake tract including those six small PCV system ports. This in turn causes reverse flow on the PCV valve. Assuming the internal PCV valve is working properly, this causes the PCV valve to close. It functions as a reverse flow check valve and a forward flow volume restrictor. In this mode, if piston ring blowby is high enough, crankcase gases are vented out through the PCV flapper valve and into the rear turbo inlet. These gases are typically laden with moisture and the PCV accordion pipe fitting that connects to the rear turbo inlet pipe creates a venturi effect under high turbo flow rates. This venturi effect causes a pressure drop which aids in evacuating the crankcase gases but also causes a temperature drop (Gay-Lussac's Law), which under the right conditions can cause ice to form at this nozzle. If ice builds up it can block the port or pieces of ice can break free and potentially damage the turbos. This is why there is an electric heater in this nozzle.

I would be curious to determine how far the previous owner took this PCV modification. Did he block the 6 PCV head ports and eliminate the vacuum side PCV mode? You can check this by putting your finger or a balloon over that exposed PCV flapper valve fitting and seeing if air is being drawn into the fitting when the engine is idling. If it is, then you definitely need to put a filter over the end of that exposed pipe (K&N makes a variety of different size filters for this application). Or just reconnect it back where it is supposed to go and put an oil catch can on the line to help remove some of the oil that makes its way to your intake valves and forms carbon buildup there. But in my opinion this is a minor player in the intake valve carbon buildup unless you have a lot of piston ring blowby. Most of the intake valve carbon buildup comes from those six small ports in the head drawing oil vapor laden crankcase gases through the internal PCV valve.

You can find images online of what I describe above by searching Google Images for [N54 PCV]. I'm sure there are Youtube videos showing this info as well.