Newbie Turbo Operation Question - bear with me

[russianwol]

Hi, I feel stupid asking this but I can't seem to find detailed enough description of how turbo works in order to answer these questions. BTW I have a 1992 W140 300SD, OM603 engine.


Does turbine simply not spin under lower RPM because the pressure of exhaust gas is not enough to turn the turbine? Or is waste gate always open and closes only when boost is needed? - this is the stupid question as what I read is that waste gate always opens when boost is too high. So what happens in low RPM/no load? Is the turbo designed to let exhaust through it without spinning at low RPM?


Another question.
There are 2 pressure lines that feed into a air pressure sensor. One comes out of intake manifold and can be called a boost pressure. The other is coming out of ALDA but they are joined together by a "Connection" with "Restriction" on the ALDA side connector. Anyone knows why?

In oder to install boost gague - would I tap into the ALDA line, Intake Manifold Line or line that goes to the sensor? Or should I have 3 gauges to get a better read?


What is the purpose of the "air flow sensor potentiometer"? It's a flap thingy in the air intake, pass the filter in a weird compartment that also has the air flow/temperature sensor. I mean there's a gate that looks like is spring loaded. Does the gate open by a way of some actuator or by simply force of air sucked in by turbo? Does the potentiometer report the "air mass" to EDS based on how wide the flap open?

There is a vacuum line called "a" - fresh air to passenger compartment. I don't get this. How is that line delivering fresh air if it's a vacuum line? Or does it simply control some sort of transducer? In my case it's not connected to anything which worries me.

Please see pictures for reference.