S4 JJL

I have a 00 S4 build date 9/99 and I have a faint siren sound between 2k and 3k on the tach, again modulated by throttle and load. I have full boost, and it does get quieter as car heats up.
At about 3k miles I detected less power and found the L type TBB to have a small tear, and replaced it with the newer T type.
It has been debated here that an intake leak can lead to overspinning the turbos, I agree this may be the problem, which happens because the ECU requests more and more boost and the turbos overspin to compensate for the leak.
Now if I used a separate boost controller with the dial set at a certain point, say 14.5 psi according to a gauge, with this type of system if there is a leak, the controller will not close the wastegates further to create more boost, as it is a fixed position bleeding vaccum to keep the WG closed to the point you set it at using a separate boost gauge, whereas the ECU controlled boost can read boost levels and keeps asking for more and actually modulates the WG in it's attempt to create the boost it wants to see.
I experienced this on my old Eclipse GST, when an intercooler hose had a small leak, and I simply noticed less boost on the gauge. I ran a 16 G unit which could generate up to 24 psi, and I ran about 17 psi on the street, had I manually adjusted the **** to compensate for the leak, I am sure the turbo could have compensated, but it would have overspun, eventually failing.
Could this be a solution? do I have this right, or am I wrong about how this works?

NASA racer

my car had a minor wastegate problem and I took it to a dealer who dropped something into the intake while they were examining it which impacted the impeller blade and blew up the turbo then another dealer did the turbo replacement and it ran fine until today when all hell broke loose and either a major boost leak occurred or the replacement turbos failed.

Sorry I just had to vent.

PhoenixGTS

ECU's boost control. If you had say a Greddy Profec A that you set to one bar, and the leak was causing you to lose say 4 psi at a given rpm, the boost controller would be aiming for 14.5 psi while the turbo would be blowing enough air so that it would be making 18.5 psi without the leak. In other words, the boost controller will still not "cap" the work the turbo does, only the amount of boost going into the engine.

VonK :: Retired

Amen.