Manifold Pressure Fluctuation

[Pabloecanales]

Last week I flew my Lycoming TIO-540 up to 21,000ft

 

But right after crossing 19,000ft the manifold pressure started fluctuating between 24in and 30in every time I pitched the nose up or down.

Without even touching the throttle.

 

On lower (normal) altitudes that never happens, Manifold pressure stays constant.

 

Is that normal due to the high altitude? Or what could be causing that

 

 

Sent from my iPhone using Tapatalk

[N201MKTurbo]

You went from a controlled boost to open loop. The waste gate was fully closed. When the engine was lightly loaded it will make more boost (MP) when it is more loaded it will make less boost. Kind of backwards from what you want. You exceeded the critical altitude for your system. It won’t hurt anything, you just have to expect it.