Do it at your own risk!
PCV valve(Positive Crankcase Ventilation valve)，不是PVC(Polyvinyl chloride -
PCV valve，我有一个最简单粗略形象的解释：如果你知道早期的高压锅，那PCV valve就是高压锅上的减压保险阀，高压锅代表发动机。
PCV如果堵塞，导致发动机内压力升高，engine oil 寻求薄弱部位突破，是引起valve cover gasket leak的原因之一。
这里有网上抄来的详细解说:
---维基百科---
As an engine operates, high-pressure gases are contained within the combustion chamber and prevented from passing into the crankcase (containing the crankshaft and other parts) between the side of the piston and the cylinder bore by piston rings which seal against the cylinder. However, some amount of gas always leaks past the piston rings into the crankcase. This amount is very small in a new or properly rebuilt engine, provided that the piston rings and cylinder walls are correctly "broken in", and increases as the engine wears. Scratches on the cylinder walls or piston rings, such as those caused by foreign objects entering the engine, can cause large amounts of leakage. This leaked gas is known as blow-by because the pressure within the cylinders blows it by the piston rings. If this blow-by gas could not escape then pressure would build up within the crankcase.
Before the invention of crankcase ventilation in 1928, the engine oil seals were designed to withstand this pressure, oil leaking to the road surface was accepted, and the dipstick was screwed in. The hydrocarbon rich gas would then diffuse through the oil in the seals into the atmosphere. Subsequently, it became an emissions requirement as well as a functional necessity that the crankcase have a ventilation system. This must maintain the crankcase at slightly less than atmospheric pressure and recycle the blow-by gas back into the engine intake. However, due to the constant circulation of the oil within the engine, along with the high speed movement of the crankshaft, an oil mist is also passed through the PCV system and into the intake. The oil is then either burned during combustion, or settles along the intake tract, causing a gradual build-up of residue inside the inlet path. For this reason many engine tuners choose to replace the PCV system with an oil catch can and breather filter which vents the blow-by gases directly to atmosphere and retains the oil in a small tank (or returns it to the sump), although this technically fails to meet most engine emission legislation.
倒腾我的老福特，保养手册读了又读，猛然发现厂家居然提到定期更换PCV valve。鉴于其可能和发动机抖动存在相关性，零件也极端便宜，所以毫无疑问要下手整这个。
相关安全措施：停车，熄火，拉闸，断电，眼镜，手套，口罩。不一定每次全用上，自己看着办。
我见过朋友烤肉的PCV，就在发动机壳右上角，很容易用Ratchet Wrenche搞下来。老福特就不一样了，PCV是藏在发动机壳的后上方，虽然没有螺丝口，但是比较难下手。打开前盖，灯照的范围是我搜索方向。哦，你看见右前轮fender上那个瘪膛(dent)啦?那不是我干的，不过是我未来的DIY目标之一。
图正中间那个白色的冬冬 --- PCV valve
三通结构，下边PCV，上边左右分处两条管道，进入左右intake.
新PCV，换成金属了。$1还是 $2，忘了。
需要两只手操作空间，左手从下边固定，右手从上边拔管子。发动机上的塑料盖子需要拆掉。
移开塑料盖，两个intake黑管子之间的空间暴露，足够右手向后下方伸进去。
正前方看过去。PCV的两根管子分别连接在左右弯曲段的intake管子上。
Throttle 和intake. PCV就在后边。
左手从这一侧伸过去抓住，右手从上方下来，拽住三通结构，摇晃几下，顺利拔出PCV(图中间白色的小东西)。
这一侧看过去。已经拔出来的PCV从intake 之间暴露出来。沿着两根管子，很容易找到与intake 的连接。同样拔出来。
PCV和管子移除后，留下的PCV接口。是下边那个。上边的不是接口，只是一个塑料外壳上的多余结构。估计是加工用的，网上很多人询问过这里是否丢了什么管子。
PCV三通和管道
新旧PCV
比较。旧的PCV有点脏，但是里边的小活塞活动看上去正常。
dust cleaner清理疏通管道。其实打气筒就够了。这么粗的气管，堵塞的可能性很小。
新PCV安装。我先连接两根管子到intake.
最后把PCV坐死。我的车型不需要固定卡子。
液体二氧化碳dust cleaner，也是居家DIY很常用的工具。pop dent也用得着，只不过我的dent不太好搞。
