The yacht is fitted with two Caterpillar C18 engines. The starboard engine will not achieve an engine speed above 1200 rpm. The local Caterpillar dealer has been struggling with the engine for months with no success and finally the engineer removed a blind plug from the turbo charger and fitted a ball valve in it's place which he left slightly open as seen in the image below. With this solution, the engine now achieves an rpm of 2300. However, I am not convinced this solution of fitting a relief valve to the turbo charger makes sense and cannot be a final repair to the problem. Something must be causing the problem and lack of performance. Any idea what the problem could be and why is the engine now performing as it should with the ball valve fitted to the turbo charger and left slightly open? Thank you.