Yanmar loses RPM's....

[dunn6253]

While out fishing yesterday, the boat started to develop a problem. Cruising at 2400 RPM's, it would slow down to an idle gradually. When this happens, there is heavier then normal black smoke coming out of the exhaust. The discharge water coming out of the boat is black, looks liked it is filled with carbon soot. To me it seems like a problem with the turbocharger system, but I come from working on diesel trucks and not marine engines.

The engine is a 500 HP yanmar 6ly2. I can get the exact model if needed.

We changed fuel filters while out at sea with no difference. When you take the boat out of gear and turn the engine up, it reaches past 2800 RPM's no problem, without any black smoke. So it only occurs when under a load. The injectors were just checked by a yanmar shop last week, and they were all given a clean bill of health.

Any idea where to start, anything you guys have dealt with before? Didn't know if this could be a common problem you guys have dealt with before......

[BahamaLure]

Black smoke indicates too much fuel or too little air, white smoke is the opposite.

Have you cleaned the air sock on the turbo?

Have you cleaned the turbo itself with water mist? Brake cleaner?

Is the intercooler clean? They gum up pretty good after a few hundred hours. You would need to exchange the core or have it professionally cleaned, it has to come off the engine to do this.

Is the inlet manifold clean? that accumulates yuk too.

There is also a little diaphragm on the inlet manifold that sends an inlet air pressure signal to the fuel rack, if this is clogged or worse, torn, the signal will never indicate full inlet air pressure and therefore never tell the fuel pump to put in quite enough fuel.

Are the inlet manifold bolts all tight? They need to be torqued down periodically, if not they will loosen and let out inlet air, this will also lead to burning out the gaskets causing worse air leaks.

All of the above has happened to me!

[Questsportfishing]

after you have it off look at your turbo fins. note if they are black and if they spin and use a good glove the fins are sharp. check all your hoses. how many hours do you have since any cooler work? check your fuel also if you have not run your boat in a while. there are good fuel polishers that are not expensive and 'cetain' plays a big part in Jap engines (Yanmar / Hino) the fuel can play havoc with these. K&N makes great filters that can replace yanmar socks by the way. we had silencer housing rivits go down turbo fins once so I started getting a crash course .. but I like them. filters and fuel are very important though.

[dunn6253]

While out on the water when the problem was happening, we took off the silencer to check out the turbo fins on the inlet side. They looked fine and spun freely with no resistance. We also changed out the fuel filters out there, with no change. Thanks for the ideas guys, hopefully she will be running right soon......

[strikezone2]

Why were the injectors checked last week

[seapower]

PM sent. Frank

[Chopsticks]

Having the same issues minus the black smoke. Any updates on this. Anybody know any great Yanmar techs in MA? Looking to get back out to the edge as soon as we can, but these issues have plagued us the last few trips out.
Thanks

Chopsticks

[aloop]

Did you use a Yanmar oil filter or after market Napa/Fram type brand? The wrong filter can cause the oil to thicken up clogging and overheating the intercooler. If you have a wet exhaust then the oil will wash out and you would never know until it's too late!

[Absolute]

The repeating the I have had with Yanmars was the exhaust mixing elbow. It would cake up with carbon, reduce the exhaust port opening and cause a reduction in rpm's overtime. I normally replaced my every two years - bought one kept the old one, boiled it out and replaced the one on the engine with the one that had been re-conditioned. Minimized cost and improved proformance.