Valve seals and boost leak

[alice]

I have read just about every post after a search for "valve seals" and I didn't notice anyone with bad valve seals saying they had a boost leak. Here are the specifics: I have a boost leak tester and when I use it to check for boost leaks, I hear nothing leaking except from within the valve cover. I also have only 12in/mg vacuum at idle and all of the other symptoms of bad valve seals ie: smoke at idle etc. So, I am looking for a few opinions on my "boost leak from bad valve seals scenario" as well as if anyone else has had a loss of vacuum from bad valve seals? Thank You for any help

 

[95CarbonEclipse]

Did you check your PCV valve?? That's probably why you're hearing a boost leak coming from the valve cover. The PCV valve for our cars and POS!! Oh yea, if it is bad DON'T BUY A NEW ONE FROM SCHUCKS/AUTOZONE. Go straight to the dealer or better yet check out the thread titled "Stupid PCV Question." You'll learn a lot.

I'm willing to bet that this isn't your only boost leak, due to you saying that your idling at 12in in vacuum. But, once you fix your PCV valve, the other leaks will become more prominant. I've got a 10% leakdown coming from my valve stem seals as well, but my boost is running just fine. Leaky valve stem seals will not show up on a boost leak test.

 

[Dream On]

I'm in a similar scenario. I installed a check valve inline with my good pcv valve, and I still have air entering under the oil cap. My vacuum isn't as low as yours (12-15) though. I'm still trying to isolate other small leaks though to see if I can get most leaks fixed.

 

[alice]

hey, thanks a lot for a super quick reply. I replaced the PCV valve soon after I bought the car thinking it would help the vacuum and it did but only 1in/hg to a fairly steady 12in/hg. However, I replaced the PCV valve with a new one from autozone and used it. There really wasn't too much of a difference between stock and new so I used the new one anyway and saw minor improvement. Also, the guy at autozone told me that my problem sounded like valve seals which is what got me going on the valve seals thing. However, its seems like if the valves were slightly open and the valve seals were bad, there would be a boost leak or at least some kind of pressure loss. I am going to check the timing in the next couple of days and see what comes of that for the vacuum problems, then gaskets.

 

[alice]

DreamOn, can you hear leaking from any spots other than the PCV/oil cap area? I can hear leaking under the valve cover pretty much centered on the intake side. I figure if you find the biggest leak first which should happen because it would be the loudest, then there will be more to come and for the most part, I am in the first step finding/fighting the biggest leak.

 

[Dream On]

I can't hear it from anywhere else except under the oil cap. I still have to check my boost gauge line, brake booster, and a few of the vacuum line connections.

 

[alice]

Is it certainly not possible to have a boost leak as a result of bad valve seals?

 

[Auto RS T]

A boost leak from under the valve cover can be:

PCV Valve, Valve Seals, or Piston Rings

 

[95CarbonEclipse]

The best advice i could give you if you want to find out why you're burning oil, and not sure where it's coming from, is to get a leakdown test performed.

If you replaced your PCV valve with an Autozone one then i'm 99.9% sure that it's leaking. They leak right out the box. Try disconnecting your PCV valve (keep it connected to the IM) and put your thumb over the valve to plug it up and see if it's leaking.

 

[luvmygst]

I have a friend that works at autozone trust me all of there pcv valves leak. I tried to be cheap and get one and I could not even find one that you couldnt blow through in both directions. Go to the mitsu dealer and but one its worth the money for one that works.

 

[95CarbonEclipse]

I have a friend that works at autozone trust me all of there pcv valves leak. I tried to be cheap and get one and I could not even find one that you couldnt blow through in both directions. Go to the mitsu dealer and but one its worth the money for one that works.

That's been my expieriance as well, do yourself a favor and get yourself a check valve to put inline from your PCV to your IM. This will take pretty much all the stress off your OEM PCV valve allowing it work properly for many, many miles. Even the OEM valves are POS really. But Autozone/Schucks valves NEVER work.

 

[alice]

Thanks for all the replies. I am going to get an OEM PCV valve tomorrow at local mitsu dealer and run a inline check valve. Of course I will be sure to properly destroy the shotty Autozone valve first. I will up date as soon as I finish.

 

[romeen]

Air can leak into your crankcase from many spots:

1) PCV valve as mentioned. To test unscrew PCV from valve cover but leave it hooked up to the vacuum hose/IM. Pressurize intake and check for air leaking past PCV. From my experience most oem valves start leaking around 10 psi. Parts store valves tend to start leaking immediately.

2) Turbo seals. If testing from the compressor inlet some leakage is inevitable since there is no oil pressure to help seal it. Don't worry about this too much unless the amount seems very excessive. To avoid this test from a point after the turbo (TB elbow, IC piping, etc.)

3) Past the piston rings. To minimize this you can do the leak test on a warm engine. Don't burn yourself. If you suspect this is a problem then do a compression test.


There are certainly many other spots that you can have a boost leak but they should not allow air into the crankcase. If you believe that your valves are not forming a good seal with the valve seats then do the leak test with the motor set at 30* ATDC to avoid any valve overlap. Pressurize and check for air escaping out of your exhaust/tailpipe. If yes then do a leakdown test to confirm.

I'm not sure if leaking valve stem seals will allow air into the crankcase. If it's the exhaust valves then your car would be smoking heavily. Any pressure should take the path of least resistance which is out through the exhaust.

Hopefully I am not missing anything obvious (I'm pretty tired right now ).

 

[Dream On]

Valve seals can definitely let air in the crank case. I leak tested my car at the TB elbow (so it couldn't be the turbo) and removed my pcv which also had a 120psi check valve in place so no air came back through, and I still had air under the oil cap and coming out of the valve cover breather. This was at 30* ATDC also.

EDIT: I pulled the pcv out to test if the check valve was working and it was. I did the test with the pcv disconnected to the valve cover also and got the same results. I have good compression also. All numbers around 165-170 psi.