OEM PCV Valve Study
The PCV valve is a pretty simple device, but it performs a potentially critical function.
It is, essentially, a regulated vacuum leak, drawing contaminated air from the crank case, rather than letting it vent to atmosphere, as in days gone by.
If you look at old pictures of roads and highways, you will notice a dark stripe in the middle of each travel lane. That's mostly from crank case oil vapors condensing in the breather tube, then dripping onto the road. It was called a "road draft tube" because it hung down enough to create a small vacuum as the vehicle moved through the air.
Air was draw into the crank case through a filtered oil filler cap on most vehicles back then.
Since the 1960's, the crank case gasses have been pulled into the intake system, to be burned with the fuel/air mixture.
Here is a picture of the PCV valve used on the Jeep JK.
It's about 1 3/4" tall.
This is a picture of what's inside the valve. Crank case vapors are draw into the hole in the bottom, pass by the tapered cone, out the top, and through the hose connected to the intake.
In the picture, the valve is in the low vacuum, high load position. It is open to allow the most flow, because under load, the intake is producing the least vacuum, but the engine is producing the most blow-by into the crank case.
In this view, valve is in the high vacuum, low load position. The tapered cone is drawn up, into the exit hole, to restrict flow, because the engine is producing less blow-by vapor. It also decreases what the engine would see as a vacuum leak.
Oil is continually being thrown around inside the crank case, producing an oil mist saturated atmosphere. If the PCV valve were to remain fully open during times of low load/high vacuum, this oil mist would be drawn out, too. An increase in oil consumption may be observed, along with a rough idle because of the vacuum leak.
This view shows the air hoses for the PCV system. A hose is connected from the intake to the PCV valve. As air is drawn out, it is replaced with filtered air from the intake box. Clean air is constantly flowing through the crank case.
Pictured is the location of the PCV valve. It is tucked away behind the coil pack.
This is how I easily removed and installed the PCV valve:
Removing the coil pack is easy to do, and greatly improves access to the PCV valve.
It may not be necessary to pull the plug wires from the coil pack, as it may drop completely out of the way.
If it doesn't drop out of the way....
Disconnect all six plug wires at the coil pack. The stock wires and the coil pack terminals are numbered, so no need to worry about marking them.
Remove the two bolts marked with yellow arrows.
Leave the main electrical plug, marked with red arrow, connected.
Rotate the coil pack up and out of the way. It will tuck in behind some of the wires, and stay there.
Now that you have plenty of room to work, remove the clamp from the PCV hose. Pliers will do it, but a hose clamp tool designed for this type of clamp will make it easier.
You now can see the PCV valve recessed into the adapter.
Put a zip tie on the neck, as pictured. Make sure it's a good, strong zip tie, and is tight around the neck.
Grab the zip tie with some pliers. Rest the nose of the pliers on the intake manifold, as in the picture.
Pry up with the pliers. The valve comes out so fast and easy, it actually may make a "pop".
Place the new valve in the adapter. It will be hard to push home, so get a socket just big enough to fit in the adapter. The socket wall should be thick enough so it will push the valve, and the rubber seal.
An extension on top, long enough to stick above neighboring lines, will allow you to push or tap the valve home.
Here is a pic of the valve after seating it with the socket.
Reconnect the hose with the clamp, to the PCV adapter.
Reinstall the coil pack, connect the wires to the appropriate terminals.
When you push the plug wires onto the terminals, make sure you hear them snap into place.
Remove all tools from the engine bay.
Very detailed write-up! What's funny is this post hit me with deja-vu from my engines class while going to school for Agricultural Engineering. I can recall sitting in class talking about the dark stripe down the center of the roads. As a youngster I assumed it was normal engine oil leaks (everything my parents owned took 2-3 quarts of oil per 3000 mile change).
How do you remove the PCV valve and is this something that needs to be replaced regularly? I know my last car ran through PCV valves every 60k miles or so, and to remove it, you just yanked it out.
The valve needs replacement when inspection indicates it is bad. Bad means the spring is broken, or the cone is frozen (not free to move up and down).
Below is from the 2008 owner's manual. Your manual may be different.
"Check the PCV valve, replace if necessary. Perform
the first inspection at 60,000 miles (100 000 km) or 60
months. 30,000 miles/30 months thereafter.
"Proper operation of this system depends on freedom
from sticking or plugging due to deposits. As vehicle
mileage builds up, the PCV valve and passages may
accumulate deposits. If a valve is not working properly,
replace it with a new valve. DO NOT ATTEMPT TO
CLEAN THE OLD PCV VALVE."
Great write up ronjenx....
Thanks for all the detail! This has been on my mind lately, thumbs up bro!!
Did this last night and it did not come out very easy. Mine was STUUUUCK in there. Tried different cable ties as noted in the writeup, but they just kept breaking or would slide of the end. Finally got it out though. I had trouble finding a place that carries the PCV valve for a JK in stock (O'Reilley's, Advance Auto Parts, AutoZone all show no PCV valve even in their systems for a JK) One guy even told me, those engines don't have a PCV!
I found a few links to part numbers online that I took by one place and they said they would have to order it. I said ok and ordered it. When it came in it really didn't match up well :)
2008 JEEP WRANGLER SAHARA 3.8L 3778cc 231 cubic inch V6 FI (1) OHV Emission : PCV Valve Auto Parts
Here is the pic of what I got for part number PCV406 on the left and the correct PCV for the JK on the right...
Soo.... after I pulled my PCV valve I took it in and we tried to locate a match. Found one that is "Almost" identical. Part number PV773.
Got this guy installed and back together and everything is running great now. Does anyone else have the appropriate part numbers for the OEM PCV?
Why didn't you get one from the dealer? They are fairly inexpensive.
The OEM part number is 04648973AB.
I looked up the Purolator PV773. It does look like the one used in the JK. Very good price at under $3.
The application list showed it is for older GM and Ford, vehicles. No evidence it is suitable for the 3.8L JK.
The difference could be the spring tension, the weight of the tapered cone, or the size of the orifice.
Oh and also, be sure to keep the black rubber fitting that is on the OEM PCV valve as I had to transfer it to my new one...
There is one dealer in my area but it is about a 45 minute drive there and I always try to not involve a dealer if possible. Thanks for the OEM part number though! I've got it saved now.
Cool, found this:
This needs to go in the FAQ :thumbsup:
I just picked up a Purolator PV773 PCV valve (less that $3) and did a comparison between it and the OEM valve.
Here is what I found:
(1 pound = 453.59 grams)
OEM valve tapered cone @ 1/2 compression = 80 grams; full compression = 165 grams.
PV773 valve tapered cone @ 1/2 compression = 170 grams; full compression = 380 grams.
The two tapered cones are of equal length and major diameter.
The OEM taper covers over 1/2 the length of the cone.
The PV773 taper covers 1/4 the length of the cone.
The valves' holes the tapered cones protrude into are of equal diameter and equal distance from the bottom of the valve.
I don't know whether or not the PV773 is a suitable sub for the OEM valve.
I do know PCV valves are calibrated for the engine they are designed to be used in.
The air flow at various power settings is the key parameter. I have no way to check that.
So it's up to the individual.
About $3 for the unknown characteristics of the Purolator valve, or about $9 for the OEM valve.
I'll def be going with OEM if I have any probs with this one and when the next maint change comes. I'll post up if I notice any changes or have any problems with this other one.
Thanks for the comparison, you wouldn't happen to be a science teacher by chance would you? This is starting to remind me of Mr. Wizard :)
Don Herbert (Mr. Wizard) passed away in 2007 at the age of 89.
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