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PCV leakage - bad part?

spoulson

Well-known member
Joined
Feb 5, 2003
Messages
2,908
Location
Worton, MD
In another thread, I did a boost leak test on my car and found that the engine crankcase was getting pressurized. I tried removing the PCV from the valvecover and left the other end attached to the intake manifold. Yep, it was leaking terribly. I was expecting the ball value to be pushed shut by the air pressure and not let any air get through.

So I spent a few bucks and got a new one at NAPA. I did the same test and found this one leaks just as bad!

Is OEM the only way to go? I have one on order from a Dodge dealer but I won't have it for a week.
 

the pcv valve should open when pressurized that's what it is made to do. try doing the boost check before the intake manifold.
 

s_firestone

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Joined
Jun 27, 2002
Messages
1,610
Location
Park City, UT USA
Correct me if I'm wrong. Have I got this right or is it backwards?

The PCV in a turbo should act like a two way threshold check valve. It is a fresh air supply that works in conjunction with the valve cover vent to evacuate blow by gas and release pressure. Under boost however it should snap shut(or at least minimize the pressure) so that you don't pressurize the crankcase faster than the vent can allow the pressure to escape. Technically under boost the valve cover vent is at a vacuum to the outside pressure and the intake, this is where the blow by escapes to, to be mixed with the intake air and unburned fuel, reburned. This is also the overwhelming reason our intake ends up covered in oil residue(no breather filter like on carbureted systems). At idle the intake vacuum is higher than the vent vacuum due to the TB butterfly being closed and unless the flow is stopped or impeded, its still a massive(but controlled) vacuum leak(only with air thats already been metered by the ECU).

There is an interesting thread on this on one of the Honda forums here.

This thread ought to make for some interesting discussion. The service manual omits all mentions of the PCV valve operation in the vacuum/emissions diagrams except in the 3 pages devoted to testing it(none of which differentiate between turbo and NA).
 

Right. When not under boost, vapors from the crankcase are pulled through the PCV valve into the intake to be burned. Once you pressurize the intake manifold the PCV closes to prevent pressurizing the crankcase and crankcase vapors are sucked through the valve cover vent by the vacuum created in front of the turbo.

So if you blow air through the threaded end of the PCV valve it should flow freely. But if you blow through the unthreaded end it should close.
 

spoulson

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Joined
Feb 5, 2003
Messages
2,908
Location
Worton, MD
For the records, it looks like the OEM PCV was the way to go.

With the new NAPA PCV I was able to blow into the manifold end without much blockage, just like the old Autozone unit I removed. The intake pressure test confirmed this leak bigtime. I couldn't get over 1 bar from my compressor tank.

For ~$2 more, the local Dodge dealer's OEM PCV, I was not able to blow through the manifold end. The pressure test confirmed little to no air leakage, even at 1.5 bar.

This should solve the oil coming out of the seals and onto the xfer case, clutch, and valve cover spark well, as well as popping the dip stick out. After a few days of driving the clutch stopped slipping. I even noticed less occurrance phantom knock, though there's still room for improvement.
 

ktmrider

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Joined
Sep 10, 2007
Messages
3,128
Location
Tempe, AZ
Ok, revival of an oldie but goodie.
Been having some annoying oil leaks for the last few months that steadily got worse ( from one drip per week to daily ). Most were from the VC half moon but upon further inspection there was oil on the bottom of the front engine cover and the top of the turbo. Replaced the oil feed crush washers but still continued to seep. Decided to replace the VC gasket ( again ) yesterday.
While replacing the gasket I recalled the AutoZone/Fram PCV valve I installed before smogging the car right after purchase. Removed it from the VC, no blockie of air in either direction.... /ubbthreads/images/graemlins/banghead.gif
The non-OEM valve was probably good for awhile ( had boost issues for a few months due to cracked EM ) but once I hit 12+ it was a matter of time before failure. It also might explain my dipstick pops but no blue smoke or vacuum issues.
Now I gotta hope the seals in the front cover are not toast.
Moral, follow the sound advice of using an OEM PCV. Cost $11 with tax at my local MMC dealer and may be the best money spent so far.
 
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