Issues with Detroit 6-71Ti engine

I would be grateful for any thoughts on an issue i am having with my port engine on my Viking 44 aft cabin. Some background so you can better understand why i am seeking advice here. I live and work in Papua New Guinea and live aboard my boat. one of the major issues here is the total lack of competent tradespeople let alone anyone who understands detroit engines. i was cruising over christmas and i noticed that the port engine was losing rpm when running on the syncroniser but after i turned off the sync it ran ok on its individual throttle. about 20 nm from home the port engie began to lose rpm again and continued to do so and to blow a lot of black smoke. i shut it down and ran on the starboard checked oil levels (no oil loss) then waited another half hour, checked again still no reduction in oil) got back to the marina to a gale blowing and tried to re start the port engine to allow me to get back into the berth but it continued to drop rpm and i noticed oil or black scum in the wake. managed to man haul the boat into the berth but now i am stupmed to understand what happened. i wondered if anyone on this site could offer me an opition as to what could be the problem. the boat seems to get a thick coating of exhaust soot and i was not sure if that could be a symptom. i may have to fly a detroit mechanic from australia to look at it but would be glad to have a thought as to what could be the problem. any advice or opinions would be gratefully received.

Thanks Marmot, the engine has walker airseps on it, i will take the filter off tonight and have a look at the turbo. Many thanks for your response i very much appreciate your taking the time to give me your thoughts.

Just some additional information. I went to the boat at lunchtime and started the port engine and it started and idled ok, i advanced the trottle to about 1500 rpm (maximum rpm is 2500 with 2200 recommended cruising) and after shutdown checked the rear and found quite a lot of soot floating on the water. it was dry and floating and for the short period of time that i ran the engine it was quite a lot. on my recent trip i had to run the engines at about 1400 rpm or about 11kts to save fuel as there was no refueling available and i wondered if this could have caused the problem. grateful again for any views.

Thanks again Marmot if i run the engine to the higher rpm, what should i look for and how can i determine if it is the turbo that caused the problem. i tried to have a look into the airsep at lunchtime but i didnt have much time. i guess what i need to do is to establish to as reasonable point as possible, what may be wrong and to try to source both the parts and labour to rectify it. i wondered if the problem may have been due to low rpm over a long period which caused the drop in rpm during the journey.

thanks jhall, i recently put brand new air filters on the airseps and oiled them so i think they are ok. i will check again later. than you very much for your feedback

Thanks Jhall,you were right! I checked the air filters and found that the filter on the troublesome engine had collapsed after being clogged up, it was new one month ago so i definitely have an exhaust leak from somewhere. I am not sure how to check for a leak but clearly it has to be fixed because replacement filters have to be sourced from the US and it took almost a month to get these ones. I am really grateful to all who responded to my post, I am relatively new to big boats and in this country it is very isolated and when a problem arises, you are on your own. it is really great to see a forum with so many people who are generous with their time and thoughts.

Thanks CaptJ, i will try the paper towell tonight and see if i can locate the source of the leak. the air filter has completely collapsed and my experience with them before has been that its a major effort to get them back in shape for continued use. many thanks for your and other member's wise advice.

thanks Mr Hall,
yes the turbo is very sooted up and I have already picked up one 20ltr drum of oil (even finding enough of the right oil here is difficult) to change the oil. is cleaning the intercooler something that i can do myself? I always try to learn about things because here you cant depend on anyone else so is there a site or how to do guide on cleaning them? Please excuse my ignorance in many things mechanical, my career has been mostly law enforcement and for the past 14 years in developing countries on poverty reduction projects so i havent had so many opportunities to get my hands on engines. This website offers me a great deal of support and for that i am grateful. my next challenge is to clean the intercooler and turbo, locate the exhaust leak, change the oil and filters and then hopefully not crash the boat into the nearest reef when i finally get it back into top condition.