Caterpillar C18 Engine Problem

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.

Thank you Captain Ralph. They do have the proper diagnostic tools but I doubt they have the ability to use it. We replaced the pressure sensors but the waste gate was not checked.

Correct, the engine is fitted with two turbo chargers. I will check both waste gates. Should be a simple fix. Thank you Captain Ralph for the suggestions.

I was told that waste gates on Caterpillar engines cannot be replaced and the complete turbo charger will need replacing if a waste gate has failed. Is this correct?

Thank you Gentlemen for the sound advice. I will have the waste gates thoroughly checked. I am very surprised the local Caterpillar technicians were not able to identify the problem.

Thank you Dockmaster for your message. The C18 engines are a 2013 model year and are C18 1150. The engine power is 1136.

Thank you Captain J. It won't be a propeller problem. She's been running well for the last 5 to 6 years. The deterioration only started in the last few months.

Thank you Dockmaster. I am having the waste gates checked and will revert.

Good luck with your installation.

Are you familiar with how the waste gate on the C18 Engine is adjusted and at which pressure does it need to start opening?

Still in process. The local CAT dealer is impossible to deal with. We removed the intercoolers and found the seals had failed and the intercooler cores were blocked with salt deposits. We cleaned them. The engine performance has improved and WOT rpm is now over 2250. The engine acceleration to 2250 rpm is normal until the coolant temperature reaches 70degc. As soon as the coolant temperature increases above 70degc, the engines start struggling going above 1200rpm.