Need some advice on an issue. 2015 R60 S is not making more than 5-6psi of boost. Car is modded with the usual bolt ons and tuned. Normally will make 20psi. Took it to a shop and they did a smoke test. Which came up with no leaks. Where should I begin in figuring out this boost loss? The shop wanted to inspect the PCV system.

 

Could be wastegate not sealing properly, or diverter valve diaphragm ripped. Neither of those will show in a smoke test.

 

Yeah I was leaning towards the diverter as it is still the stock one. Just wanted to see if there was something else I should look at first. Now to find the time to tear it apart and check it.