PCV Valve- How it works, how to replace it
01-20-2014, 12:21 AM
#1
PCV Valve- How it works, how to replace it
Why does your truck have a PCV System?
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. The pressure from this explosion drives the piston in the cylinder downward, where it causes the crankshaft to rotate. 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. Meanwhile, the rising piston pushes the air and gas left over from the explosion back out of the cylinder through an exhaust valve.
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. This escaping gas is called blow-by and it's unavoidable. It's also undesirable because the unburned gasoline in it can gunk up the system and produce problems in the crankcase. 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. Then, in the early 1960s, positive crankshaft ventilation (PCV) was invented. This is now considered the beginning of automobile emission control.
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. 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. So the blow-by gases should only be recycled when the car is traveling at slow speeds or idling. 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. 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. This is good, because the blow-by gases aren't needed when the engine speeds up. 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. Since the whole point of positive crankcase ventilation is to keep these gases out of the crankcase, the PCV valve is designed to close off when this happens and block the backflow of gases.
http://auto.howstuffworks.com/positi...ion-system.htm
How a PCV valve works
Most engines employ a PCV valve at the point where fumes are drawn out of the engine. The PCV valve serves several functions. At an idle, engine vacuum is very high, around 16 to 20 inches. This high vacuum would tend to draw oil as well as fumes from the engine. The PCV valve acts as a buffer against oil being drawn out. It also regulates the amount of vacuum applied to the engine, based on engine load and speed.
At an idle, engine speed is low, around 600 RPM. A relatively small amount of fuel and air travel through the intake at idle speed. If the PCV valve did not regulate air flow, the engine would act like it had a vacuum leak. Too much air flowing into the intake causes the engine to lean out [too much air in relation to the fuel] and misfire. At an idle, the PCV valve restricts air flow, to reduce this problem. At high manifold vacuum [idle], a spring loaded valve is drawn up and partially restricts flow to the crankcase. The first drawing above illustrates the PCV valve position at idle.
On acceleration far more fuel and air move through the engine and intake manifold vacuum is much lower. Air introduced by the PCV valve has much less influence on the fuel-air mixture. Low intake manifold vacuum allows the valve to move to a more central position. In this position the system draws more fumes from the crankcase. The additional flow is very beneficial, without affecting engine performance. The center illustration above, shows the PCV valve in acceleration position.
Any pressure in the intake causes flow in the opposite direction. This could occur during an engine backfire or if the engine is turbo-charged. The PCV valve can act as a check-valve in these situations. By closing the PCV valve, any positive pressure or fuel vapor is prevented from entering the crankcase. Even a very small amount of positive pressure can force oil passed gaskets and seals and blow gaskets out of place. Failure of the valve to seal positive pressure may damage the engine.
http://www.agcoauto.com/content/news/p2_articleid/197
What does it look like and where is it at?
It is typically located on the passenger side valve cover. Its really hard to miss.
Easy signs it is bad or stopped up? A stopped up PCV Valve doesnt allow excess gas and mositure to exit the system so oil and moisture can build up under the valve covers and create lots of problems.
How to test for a bad PCV Valve/Hoses. (The factory 90 degree elbow tends to leak alot too) remember this is a closed system and needs vacuum, so any pin hole leads can cause issues.
1) First start your truck up and allow it to idle.
2) Then remove the PCV valve from the valve cover and put your hand on the bottom of the valve and check for vacuum.
3) If no vacuum is present, remove the valve from the hose and check the hose for vacuum.
Case 1: If vacuum is felt with the PCV valve connected, the system is working properly.
Case 2: If vacuum is NOT felt with the PCV valve connect, but vacuum is present at the hose, then your PCV Valve is bad.
Case 3: If vacuum is NOT felt at the PCV valve or hoses, replace both. They are super cheap, and definitely a good maintenance idea.
If you noticed in the pictures above, my PCV Valve has two hoses going around it. This is actually a way of heating the Valve itself and is fairly useless in my opition. The hoses simple wrap around the lip on the Valve and cause more harm than good. You can buy electrically heated PCV Valves that work much better, but I dont think it is all that necessary. The two hoses wrapping around it have no effect on the vacuum. You can see in the picture below what the pieces look like and that the coolant hoses are completely separate.
In the picture below you will see a triple tree of lines coming off the throttle body housing. The one in the middle is the only one that is directly connected to the PCV, the other two are simply coolant lines.
The valve itself is this simple. Just unhook the elbow and twist and pull it from the grommet in the valve cover.
You can pry the grommet out and inspect it for cracks or wear.
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. The pressure from this explosion drives the piston in the cylinder downward, where it causes the crankshaft to rotate. 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. Meanwhile, the rising piston pushes the air and gas left over from the explosion back out of the cylinder through an exhaust valve.
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. This escaping gas is called blow-by and it's unavoidable. It's also undesirable because the unburned gasoline in it can gunk up the system and produce problems in the crankcase. 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. Then, in the early 1960s, positive crankshaft ventilation (PCV) was invented. This is now considered the beginning of automobile emission control.
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. 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. So the blow-by gases should only be recycled when the car is traveling at slow speeds or idling. 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. 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. This is good, because the blow-by gases aren't needed when the engine speeds up. 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. Since the whole point of positive crankcase ventilation is to keep these gases out of the crankcase, the PCV valve is designed to close off when this happens and block the backflow of gases.
http://auto.howstuffworks.com/positi...ion-system.htm
How a PCV valve works
Most engines employ a PCV valve at the point where fumes are drawn out of the engine. The PCV valve serves several functions. At an idle, engine vacuum is very high, around 16 to 20 inches. This high vacuum would tend to draw oil as well as fumes from the engine. The PCV valve acts as a buffer against oil being drawn out. It also regulates the amount of vacuum applied to the engine, based on engine load and speed.
At an idle, engine speed is low, around 600 RPM. A relatively small amount of fuel and air travel through the intake at idle speed. If the PCV valve did not regulate air flow, the engine would act like it had a vacuum leak. Too much air flowing into the intake causes the engine to lean out [too much air in relation to the fuel] and misfire. At an idle, the PCV valve restricts air flow, to reduce this problem. At high manifold vacuum [idle], a spring loaded valve is drawn up and partially restricts flow to the crankcase. The first drawing above illustrates the PCV valve position at idle.
On acceleration far more fuel and air move through the engine and intake manifold vacuum is much lower. Air introduced by the PCV valve has much less influence on the fuel-air mixture. Low intake manifold vacuum allows the valve to move to a more central position. In this position the system draws more fumes from the crankcase. The additional flow is very beneficial, without affecting engine performance. The center illustration above, shows the PCV valve in acceleration position.
Any pressure in the intake causes flow in the opposite direction. This could occur during an engine backfire or if the engine is turbo-charged. The PCV valve can act as a check-valve in these situations. By closing the PCV valve, any positive pressure or fuel vapor is prevented from entering the crankcase. Even a very small amount of positive pressure can force oil passed gaskets and seals and blow gaskets out of place. Failure of the valve to seal positive pressure may damage the engine.
http://www.agcoauto.com/content/news/p2_articleid/197
What does it look like and where is it at?
It is typically located on the passenger side valve cover. Its really hard to miss.
Easy signs it is bad or stopped up? A stopped up PCV Valve doesnt allow excess gas and mositure to exit the system so oil and moisture can build up under the valve covers and create lots of problems.
How to test for a bad PCV Valve/Hoses. (The factory 90 degree elbow tends to leak alot too) remember this is a closed system and needs vacuum, so any pin hole leads can cause issues.
1) First start your truck up and allow it to idle.
2) Then remove the PCV valve from the valve cover and put your hand on the bottom of the valve and check for vacuum.
3) If no vacuum is present, remove the valve from the hose and check the hose for vacuum.
Case 1: If vacuum is felt with the PCV valve connected, the system is working properly.
Case 2: If vacuum is NOT felt with the PCV valve connect, but vacuum is present at the hose, then your PCV Valve is bad.
Case 3: If vacuum is NOT felt at the PCV valve or hoses, replace both. They are super cheap, and definitely a good maintenance idea.
If you noticed in the pictures above, my PCV Valve has two hoses going around it. This is actually a way of heating the Valve itself and is fairly useless in my opition. The hoses simple wrap around the lip on the Valve and cause more harm than good. You can buy electrically heated PCV Valves that work much better, but I dont think it is all that necessary. The two hoses wrapping around it have no effect on the vacuum. You can see in the picture below what the pieces look like and that the coolant hoses are completely separate.
In the picture below you will see a triple tree of lines coming off the throttle body housing. The one in the middle is the only one that is directly connected to the PCV, the other two are simply coolant lines.
The valve itself is this simple. Just unhook the elbow and twist and pull it from the grommet in the valve cover.
You can pry the grommet out and inspect it for cracks or wear.
Last edited by ibd2328; 01-20-2014 at 06:03 PM.
The following users liked this post:
TPDM04 (02-25-2017)
01-20-2014, 12:22 AM
#2
These parts are all fairly inexpensive and need to be replaced every 50-80k or whenever a problem arises. Mine were all in good working order, just had some build up inside the valve itself holding it closed. So I used an air compressor and soaked all the parts in Kerosene for a while to clean them. DONT USE THROTTLE BODY CLEANER IT IS TERRIBLE ON RUBBER PARTS.
Once all the parts are clean, make sure to clean off the Valve Cover opening for the gromment and replace it.
I used a little bit of sealant around the grommet and PCV Valve to help, mainly bevause these should be replaced whenever you do a change. Along with the hoses connecting them to the throttle body housing.
4) Engine Coolant Temperature (ECT) sensor
What is it? How does it work?
Once all the parts are clean, make sure to clean off the Valve Cover opening for the gromment and replace it.
I used a little bit of sealant around the grommet and PCV Valve to help, mainly bevause these should be replaced whenever you do a change. Along with the hoses connecting them to the throttle body housing.
4) Engine Coolant Temperature (ECT) sensor
What is it? How does it work?
Last edited by ibd2328; 01-20-2014 at 06:45 PM.
The following 2 users liked this post by ibd2328:
jollyroger331 (01-20-2014),
white89gt (07-16-2016)
02-06-2016, 12:39 AM
#7
Excellent description of the operation of the PCV system.
Our 2003 5.4L Expedition PCV system looks identical to the parts in the pictures, except for one item. There is a Y in the line from the intake manifold to the PCV valve. The extra line goes to the rear of the intake manifold and connects to a 3/4" plastic tube in the plastic part of the intake manifold. The end of this line has one of the infamous PCV elbows that leak. The line is Ford 2L3Z-6C324-AA with heater hoses or F85Z-6C324-EA without. Every car I have seen before has one intake connection from the PCV valve. Any idea what the second connection is for?
Our 2003 5.4L Expedition PCV system looks identical to the parts in the pictures, except for one item. There is a Y in the line from the intake manifold to the PCV valve. The extra line goes to the rear of the intake manifold and connects to a 3/4" plastic tube in the plastic part of the intake manifold. The end of this line has one of the infamous PCV elbows that leak. The line is Ford 2L3Z-6C324-AA with heater hoses or F85Z-6C324-EA without. Every car I have seen before has one intake connection from the PCV valve. Any idea what the second connection is for?
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08-27-2019, 08:10 PM
#8
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Great Article on Ford Triton PCV valve
Now I know. I was recently repairing my blown spark plug and was trying to figure out what all the hoses on that side of the engine was for. Great Photos. Thanks for posting!