Air pressure in valve cover

[JOLTY TacoMan]

I have been struggling with a boost leak for the past few months now. I finally got around to buying a tester and found my bov was leaking bad and air was coming out my breather on my valve cover. Ordered an OEM replacement from STM, boost leak was still there. The leak seems to not affect performance as much on hot days. Did another BLT and found air still coming from the breather, took the pcv hose off and capped it, and air was still coming from the breather. I have read it could be valve seals. Also, my car has been pulling timing on my occasionally during normal driving.

 

[92AWDTalonTSI]

Well in order to check boost leaks all your valves should be closed. (Engine at TDC.) If they are it could be guides. Also, if a valve is still open while TDC (Bent valve.) it could be letting air into a cylinder and also by a piston, thus up and out of your cam cover.

Do a leakdown test.

If the air is coming out of the throttle body that would leaking intake valve.

If it's coming out of the exhaust, it is an exhaust valve.

If it's coming out of the breather or PCV valve the rings and or cylinders are worn.

A leakdown combined with a compression test would tell you more.

If only one cylinder has bad compression, but no leaks, it usually has a valvetrain problem such as a worn cam lobe, broken valve spring, collapsed lifter, etc etc.

If all cylinders have low compression but no leakage. (Well, no more than a 10% loss.) That indicates that timing may be off.

Do a compression test first then do a leakdown test.

 

[luv2rallye]

Two cylinders intake and exhaust valves are open at TDC: http://www.dsmtuners.com/forums/attachment.php?attachmentid=121912&d=1303187520.

 

[Calan]

Two cylinders intake and exhaust valves are open at TDC: http://www.dsmtuners.com/forums/attachment.php?attachmentid=121912&d=1303187520.
Better to set at 40* BTDC where all intake valves are closed.

This ^.

And even then, it's common for air to leak into the crankcase past the valves, depending on cams, valve overlap, etc. (I just had deja vu...I typed that exact same response just a day or two ago to an identical question . If you inject high enough pressure during the BLT, you can also blow the valves open slightly depending on the valve springs. The temperature of the motor also effects it.