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Boost Leak Test (Audio) Question


Well-known member
I'm doing a boost leak test to rectify any leaks and I think I have been successful. But I'd like some input into what this noise is in the video:


I have an idea, but would appreciate input. Background is this: roller rockers are removed on the intake side to (hopefully) ensure all the intake valves are closed and the adapter is in the intake tract where the MAS sits. EGR block off plate is in place and not leaking. PCV valve is capped and not leaking. It sounds like this is coming from within the intake manifold. FP Green turbo in good shape. Here's the setup:




Well-known member
I'm not actually hearing a obvious leak, but building up air pressure makes noise. Double check the injector seals, but leaks to me sound more like a obvious hiss.


Active member
OMG I have this noise too but when my car is running. It does it every so often and it drives me nuts because I don't know what it is or can't describe it enough. Following this thread now for an update


Well-known member
I've finished the boost leak testing, reinstalled the rockers and resealed the valve cover. I drove the car this week. I could never figure out definitively what this noise was, but my best guess is that it was air coming through the oil return line on the turbo, bubbling up through the oil in the pan. Another possibility is maybe the air from the pressurized intake tract was coming through the intake valves by overcoming the intake valve spring pressure.

Since the goal of this exercise was to identify and seal up any boost leaks with the intake tract pressurized, I feel whatever this specific leak was is normal. I just wanted to know what it was. I ended up addressing leaks at the BOV, FPR and bottom of the throttle body, among other places. I wanted to do the test with as much of the intake tract pressurized as possible (from the turbo to the intake valves), but I think this inherently results in some leakage that is normal (turbo shaft seals and intake valves).




Well-known member
Just to be clear, the sound I'm talking about (that can hopefully be heard in the video) is a pulsating, intermittent sound, not a constant hiss.