ORIGINAL: tw3ak

My pcv valve keeps blowing out of my lower intake and spits oil all over my firewall. What is causing this and how can i fix it?

ORIGINAL: tw3ak

Ithink it might have to do with my supercharger.

ORIGINAL: samseed101

Under normal circumstances, the vacuum created by the engine would suck air through the PCV valve and into the upper intake. That would clean the "bad" air and blowby out of the crankcase and it would get replaced with fresher air that will, in turn, remove more contaniments from the crankcase. Of course, the PCV valve is one-way, or at least it's supposed to be. Our PCV valves aren't meant for boost so some boost will get by the valve. But for the most part, it's one way.

So what happens when you add a supercharger? Well when you hit WOT and the RPMs start rising, the engine goes from naturally aspirated to boosted. This means that there is no longer a vacuum; instead air is getting forced into the engine. Now remember that line that ran from the upper intake to the PCV valve? Since the intake manifold is now under presure, airflow is reversed in that line as well.

Of course, if you have a good working PCV, then it will close and prevent that boosted air from entering the crankcase. But our PCV valves SUCK, so a little boost is going to get by to pressurize the crankcase anyway. Also, don't forget that there is still going to be some blowby...and now that you've increased pressure, there's going to be even more blowby than when you were N/A. And then remember that tube that ocnnects the valve covers to the throttle body? Well that's not one way. Air will reverse direction in that tube as well but this time it will actually reach and pressurize the crankcase. So now you have blowby getting into the crankcase, boost getting past the crappy PCV valve, and air being forced in through the valve covers.

Before, that blowby and excess presure could be vented through the PCV. But now since it is temporarily closed, the pressure has nowhere to go. Now it's going to start looking for a way out (seals, gaskets, or more often, the oil dipstick and PCV valve.) That is why your PCV valve and sometimes even your oil dipstick will pop out.

If you add breathers to the valve covers, this will give the crankcase a way to relieve the pressure. But then when it's running N/A you create a vacuum leak... The upper intake will suck air from the crankcase via the PCV valve. As the air gets sucked from the crankcase, it needs to be replaced. It will take that air from the breather caps, suck it into the crankcase, through the PCV, and into the upper intake... Thus introducing unmetered air into the engine...and that is bad.

A solution... remove the PCV system and convert it to a Breather type setup. To do this, remove the tube that connects the oil filler tube to the TB and cap it off on the TB side. Take the oil filler tube side and vent it to the atmosphere (or replace the entire valve cover and just pop on a breather instead.) Take the tube that connects the PCV to the upper intake and disconnect it from the upper intake. Plug the nipple on the upper intake side and let the tube (which is still connected to the PCV valve) vent into the atmosphere as well. Now add a breather to the opposite valve cover. A lot of times, people will place this tube right next to the filter on the inlet side of the supercharger. That helps reduce the smell of fumes in the engine bay and passenger compartment.

There is another method that some people seem to use successfully. It involves leaving the PCV system connected but actually running an open breather. Like I said above, that creates a vacuum leak. But some argue that it is a very small vacuum leak and you can tune around it by slightly enrichening the mxture to compensate for the vacuum leak.

To do this, you need to make a few changes. First, get a nice fresh PCV valve. Look for one off an old 4 cylinder turbo Mustang because that one is designed for boost. If you can't find that, then you can get one for a 1995 Toyota Supra which was also boosted. Just be sure to get the grommet for it too. You will also need a check valve. The cheapest way is to just get a brake booster valve.

Once you have those parts, install the new PCV in place of the old one. Then, take the check valve / brake booster check valve and place it in the middle of the vacuum line that goes from the PCV valve to teh upper intake. When in place, it should allow air to flow from the crankcase. But when pressure is applied from the other side it will prevent any air at all from getting by and into the crankcase. Now get a single open-element breather and drop it on the passenger side valve cover. By doing this, you let the PCV still suck gasses out of the crankcase during normal operation. And when you hit WOT, the check valve and new PCV slam shut to protect the crankcase while any blowby will easily be blown out the breather cap.

I am normally against creating an intentonal vacuum leak. But with some setups, it's barely noticable and you can tune around it. if you hate vacuum leaks too, then use the first method I mentioned. If any part of it is confusing, don't hesitate to ask. I spend a LOT of time dealing with MAFs and dealing with PCV systems.