Yanmar baffling black smoke
I purchased this boat, a 1981 Stevens 47, in March of 2008. It has a Yanmar 4JH2-HTE 75hp turbo/intercooled diesel engine that was installed in 1992. At the time of my purchase the engine had approximately 3500 hours. It now has about 4000 hours. It has always run great for me. It has always put out a small amount of light grey smoke at idle and under load but not anything excessive, barely noticable really. It also would put out some black smoke running at maximum rpm driving the boat at hull speed. It has never burned any oil, I do not have to add any oil between oil changes. The engine has always started very easy, on the 3d or 4th turn over when cold.
I brought the boat from St. Thomas to Jacksonville FL in June of 2009 to do extensive refit work. Since June of 2009 she has been in a slip not being run until Monday of this week with the exception of 10 minutes running to and 10 minutes from being hauled out in mid December 2009.
During November of 2009 I removed a number of ancilliaries from the engine to facilitate cleaning and painting everything. I removed the air cleaner, turbo, after-cooler, turbo oil drain tube, alternator and injection hard lines to the injectors. I stripped the engine area, treated all surfaces, primed and painted everything. The turbo was cleaned out with carb cleaner and compressed air but not at high pressure and it was not spooled up to any speed without lubrication. When reassembled, and now as verified today by hand and direct observation the turbo spins freely. Everything was reassembled and after some problems related to figuring out how to bleed the injectors so the engine would run (the Yanmar manual did not give the correct procedure) it fired right up and ran well. I did not run it under load at that point but it fired and ran normally.
When we left the slip on Monday of this week to head out cruising, the boat threw large amounts of black smoke and the exhaust water was black with soot. This was at both low rpm and under load. At cruising speed of 2400rpm the smoke and the exhaust water were very sooty black. After 3 hours of running the transom well stained with black soot.
We anchored out and I began investigating. It appeared that the oil level was higher than when we left (it was right at the full mark and after our run it was 1/2" - 1/2" above the full mark) and the oil seemed to be diluted. It did not reak of diesel, but its viscosity between your fingers did not feel like non-diluted oil. So I feel it was leaking fuel into the oil thus raising the oil level.
I called the local Yanmar dealer and make arrangments to take the boat to them Tuesday morning. I changed the oil and we motored up there early Tuesday, a run of less than 30 minutes. The engine started normally and ran fine but of course smoked like crazy.
The Yanmar dealer diagnosed a likely injector issue. They pulled the injectors and indeed they looked pretty bad. The injectors were sent out to an injector shop. They reported that 1 was all but totally plugged up, 2 others were pretty bad and only one was "decent". I had a set of new nozzles (brand new in sealed new containers) and these were used to rebuild the injectors. So we have new injectors (with new nozzles the injectors are new). At this same time based on advice received online I replaced the fuel lift pump with a new unit I had onboard. I disassembled the old fuel lift pump but did not find any obvious cracks or issues with the internal diaphragm though it was clearly old.
We ran the engine with the new injectors, new oil and filter, new fuel lift pump, new fuel filters and clean fuel..... and while the engine did idle better and it general seemed to run smoother it still threw the black smoke.
We conducted a sea trial with the mechanics on board. The maximum rpm the engine will make is 2,950 measured with a seperate tach tester and matching my onboard tach, at full throttle. Thats all she will give and at that rpm under full load she basically pours black smoke and the exhaust water is sooty black.
We tested the turbo boost and at max rpm it is about 9psi. It should be around 15psi at max of 3700rpm at full throttle. The turbo is spinning but the engine appears to be overloaded and cannot reach full rpm..... or at least that is the conclusion the techs are at right now.
We removed the valve cover checked for any obvious valve issue and turned the engine over to listen for any obvious top end leaks. The engine clearly has compression as TDC can be felt as it approaches and there is no leaking apparent or other noises. Also, even when cold the engine now starts on the first turn... it basically spins and starts immediatly. Compression certainly seems good. When running we removed the breather line and there is no pulsing or any sign of any blow-by indicated at all.
We removed the after-cooler and checked for any blockage of the intake air charge. There is none, it was relatively clean. There is no blockage in the air cleaner assembly and we ran the engine with the air cleaner off with no change in the problem. With the air cleaner off the turbo can be easily spun with the finger and no obstructions or sticking is noted. Additionally when the engine is run the turbo can clearly be heard though the techs say it is not as loud as it should be because the engine is not building the rpm and boost at load as it should (overloaded).
The engine will rev to 4,000 rpm at the dock not under load (out of gear).
The techs and the Yanmar service rep at Mastry all seem to think that issues with the fuel injection pump are pretty much impossible and that any adjustments that would effect this are not possible at the injection pump.
Checking the oil after the sea trial and running for test it is not possible to tell for sure if the engine is putting any fuel in the oil. The oil level before running seemed to be just a tiny bit over full, I just checked the oil and measured the level exactly and the oil level is 7/8" over the full mark.... but the oil does not smell like diesel and it does not feel diluted (though thats not all that easy to tell).
Perhaps when I checked the oil before not all of the new oil had found its way to the crankcase? Would being overfilled perhaps cause the cranshaft to actually spin in oil and thus overload the engine preventing it from reaching max rpm? Would this be possible with no indications of oil being throw about in the breather or such?
Can a Max-Prop magically change its pitch all by itself resulting in the engine suddenly being overloaded when before it was fine? Could some piece of trash like a plastic bag be wrapped around the max prop in a fashion such that the spurs would not cut it off but it would overload the engine while also not causing any abnormal vibration nor give any other sign?
Engine run testing and sea trial were conducted with engine space doors removed on 3 sides... she is getting all the air any engine could ever want.
Are there in fact aliens living in my bilge screwing with me intent on destroying my cruising dreams and bank account?
Baffled in Jacksonville....