Manifold Pressure line tee - where does it attach?

[JoeM]

I have a 65 M20E SN 539 with aftermarket M20 Turbo. My Manifold Pressure wouldn't go below 26", even at idle. Investigating,  I found a short line connected to the back of the MP gauge with a tee into the line that goes from the gauge through the firewall to the intake manifold. This line was dangling, disconnected and open. I tested the system and, with this line plugged, it holds vaccuum well and the MP gauge goes down to zero. If I plug the end of this short line with the engine running, the MP gauge works normally, showing 15" MP at idle. Is this tee line supposed to connect to something? I can't find a diagram in the manuals I have. Thanks in advance.

[Jsno]

QAA.com has an article on how the turbo operates.  It uses manifold pressure for the controller to regulate the turbo. Maybe the tee was the connection to that. 

[N201MKTurbo]

The M20 Turbo system doesn't require any MP connection. Mine is hooked straight from the gauge to the engine. Do you have an engine monitor that uses it?

[Fly Boomer]

2 hours ago, Jsno said:

QAA.com has an article on how the turbo operates.  It uses manifold pressure for the controller to regulate the turbo. Maybe the tee was the connection to that. 

It may depend on what kind of controller.  Different engines and their various sub-models, use different types of wastegates and controllers, so it's also important to know if the controller is an absolute pressure controller, variable absolute pressure controller, density controller, differential pressure controller, sloped controller, rate controller, or pressure ratio controller.  Not all of those are common, but they all function somewhat differently.  In one article by Paul New, he points to  the Cessna P201 and T210 where, for a certain year, you need to know the serial number and need to know whether a certain Service Kit has been installed to differentiate between three different controllers.

[N201MKTurbo]

7 minutes ago, Fly Boomer said:

It may depend on what kind of controller.  Different engines and their various sub-models, use different types of wastegates and controllers, so it's also important to know if the controller is an absolute pressure controller, variable absolute pressure controller, density controller, differential pressure controller, sloped controller, rate controller, or pressure ratio controller.  Not all of those are common, but they all function somewhat differently.  In one article by Paul New, he points to  the Cessna P201 and T210 where, for a certain year, you need to know the serial number and need to know whether a certain Service Kit has been installed to differentiate between three different controllers.

He said he had an M20 Turbos. I have one of those. I know it very well. It has a fixed wastgate just like the early 231s (exact same parts) It uses a popoff valve on the compressor side to regulate the manifold pressure. No manifold pressure connection required anywhere. If you are curious, I posted the installation instructions in the download section.

[Fly Boomer]

6 minutes ago, N201MKTurbo said:

He said he had an M20 Turbos. I have one of those. I know it very well. It has a fixed wastgate just like the early 231s (exact same parts) It uses a popoff valve on the compressor side to regulate the manifold pressure. No manifold pressure connection required anywhere. If you are curious, I posted the installation instructions in the download section.

It was just my long-winded way of saying that any generic article on "how a turbo operates" will likely omit some relevant details.

[Jsno]

Yes I used a generic article.  Just trying to point in some direction without seeing the aircraft.