Why is it bad to leave the little rubber hose that runs from the valve cover to the intake manifold?
This article is based on my understanding of the PCV system and how it works on the 4AGE engine in particular and is based largely on my personal experience with my cars. Though it may be for the 4AGE, the concepts found on this page can be used with most engines that use this type of ventilation system.
PCV tube stands for the Positive Crankcase Ventilation tube (PCV). It's used to vent any pressure built up in the head of the engine, but since we have emissions laws, that venting means that the gasses must be properly burned to prevent excess pollution. This is done by sending the gasses back into the engine through the intake. When this occurs not only will the engine have a pushing pressure, the intake will also have a sucking action working on the tube. This results in a force so great that gasses AND oil will be transferred from the engine and into the intake manifold. In other words, it results in burning oil.
The worst part about this situation is that few people realize WHERE in the intake those fumes and oil get deposited, and it is NOT directly into the middle of the manifold as assumed. The manifold itself has a passage inside of it which runs along it's side, into the front of the intake. Anything that comes through that tube will be dumped out directly into the THROTTLE BODY. If you look at the inside of the throttle body, there is a hole in the upper right side. That is where the gasses and oil come in.
What's bad about burning a little oil? As oil gets sucked in, the throttle body, intake manifold, cold start fuel injector, and T-VIS butterflies develop a thick oily residue which coats everything it touches. When the tiny particles of dust and dirt that make it past the air filter come in contact with that oil, they bond together making a thick sludge. In the most severe cases, this can lead to the complete failure of the T-VIS system when the butterflies get so gunked up they can no longer open and close properly. The bad part about getting the throttle body dirty in particular is that it has sensors within it that contribute to the info the ECU needs to properly run the engine. Those sensors can't operate properly if they're covered in an oily residue. I'm not certain how bad it is for the cold start fuel injector, but I'm fairly certain the injector wasn't designed to operate while covered in crap.
SO WHAT DO YOU DO?
Keep the oil from getting to the intake!
CATCH CAN
These containers are designed to "catch" the oil being sent through the PCV system, while allowing the fumes to continue their journey to the engine to be burnt. Cusco is probably the most famous catch can in the Japanese auto scene. But do you need a $110 US polished chrome cylinder that does nothing more than HOLD dirty old oil so it doesn't make it into the engine? Depends how pretty you want your car to be. The Cusco unit will work great, but I can think of many more useful ways to put that much money to use...hell, some people could probably buy some common sense for that much if they looked hard enough.
The way a catch can works is very simple, as it's nothing more than a can with two tubes. The more complex units may have drains, one-way valves, but a basic setup will work just as well. A picture is worth a thousand words, so have a look at the one below...
the first prototype I made for fun
the new and improved setup (never used)
This design doesn't send the fumes back to the intake and instead releases them into the air. Part #4 is used to plug the intake manifold side of the PCV system
total cost so far? $22 CAN, and yup, it's steel braided (all pretty and stuff)
1 - steel braided hose with 3/4 and 3/8 connector
2 - 3/4 to 1/2 adapter to fit onto any standard pop bottle
3 - closing spout to empty contents from can
4 - plugs intake manifold side of PCV tube/hole (part of the tube will be needed)
5 - 3/8 adapter to connect to the PCV tube off the valve cover (part of the PCV tube will be needed)
Cost can be as low as $15 or so with brass/slightly different fittings, and the hose itself will probably be returned for another which is about 2-3" shorter (and cheaper)
