Hi,
just wonder is it bad sign when air is leaking from valve cover vent hole (connecting to oil catch tank) when performing boost leak test?

No white smoke observed so far and car still able to boost.

Is it a sign of bad piston rings?

 

Well it depends on how much air is leaking out of there. Normally you will get air coming out of there because air leaks past the rings, valves etc. If you suspect that the air is leaking out abnormally i suggest you do a leak down test. Not a compression check but a leak down test. That way you can point out where the leak is coming from and if it is within limits.

 

Thanks Smoke777

Btw, what is the acceptable Leak down limit (pressure)?

Thanks