In fact, when the car is up to speed, the pressure in the intake manifold can actually become higher than the pressure in the crankcase, potentially forcing the blow-by gases back into the crankcase. This is good, because the blow-by gases aren't needed when the engine speeds up. When the engine speeds up, the air pressure in the intake manifold increases and the suction slows down, reducing the amount of blow-by gas recycled to the cylinders. Fortunately, when the engine is idling the air pressure in the intake manifold is lower than the air pressure in the crankcase, and it's this lower pressure (which sometimes approaches pure vacuum) that sucks the blow-by gases through the PCV valve and back into the intake. So the blow-by gases should only be recycled when the car is traveling at slow speeds or idling. It isn't always desirable to have these gases in the cylinders because they tend to be mostly air and can make the gas-air mixture in the cylinders a little too lean - that is, too low on gasoline - for effective combustion. Positive crankcase ventilation involves recycling these gases through a valve (called, appropriately, the PCV valve) to the intake manifold, where they're pumped back into the cylinders for another shot at combustion. This is now considered the beginning of automobile emission control. Then, in the early 1960s, positive crankshaft ventilation (PCV) was invented. Until the early 1960s, these blow-by gases were removed simply by letting air circulate freely through the crankcase, wafting away the gases and venting them as emissions. It's also undesirable because the unburned gasoline in it can gunk up the system and produce problems in the crankcase. This escaping gas is called blow-by and it's unavoidable. However - and this is where crankcase ventilation comes in - a certain amount of that mixture of air and gasoline is pulled down by the piston and slips through the piston rings into the crankcase, which is the protective cover that insulates the crankshaft. Meanwhile, the rising piston pushes the air and gas left over from the explosion back out of the cylinder through an exhaust valve. The rotation of the crankshaft not only pushes the piston back up into the cylinder so it can do all this again, but it also turns the gears within the car's transmission that eventually make the car move. The pressure from this explosion drives the piston in the cylinder downward, where it causes the crankshaft to rotate. A mixture of air and gasoline is pumped through a system of tubes called the intake manifold through each cylinder's intake valve (or valves), where a spark from a spark plug causes the mixture to explode in the open space at the top of the cylinder called the combustion chamber. Okay - one, two, three, go!Īn internal combustion engine is built around a series of hollow cylinders, in each of which is a moveable piston designed to glide up and down inside it. But to do that, we're going to have to give you a quick refresher course in how the internal combustion engines found in most automobiles work. Or at least it shouldn't seem complicated after we've finished explaining it to you. But it really isn't all that complicated. Unless you're a real gear head, just seeing the phrase "positive crankcase ventilation" probably makes your head hurt, because it sounds, well, complicated. I haven't been able to figure out what this thing is called to make any headway in searching for a replacement.Alexey Dudoladov/the Agency Collection/ Getty Images Since this car is my only way around, I was too afraid of the thing crumbling to pieces if I handled it too much, so I didn't want to pull it apart to get a better look at it. The white spot on this connector is hard and crystalline, like dry superglue: Not only are there zip ties holding the hose together, but it appears that someone's also tried to use superglue to hold it together. While inspecting closer I found this piece connected to the PCV hose near my throttle body that inserts into the air intake manifold. In preparation of changing both the hoses and the PCV valve, I was looking everything over and tracing the hoses around to see what exactly I needed to buy for replacement. I know that the PCV hoses in my car need some TLC that fact is readily apparent because someone has liberally applied zip ties to some of them to keep them in place.
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