Diesel losing power - black exhaust

[zeehag]

mike-try mixing elbow first, after air cleaner, but it sounds more like the excitement i had with my high pressure pump. aka injector pump. we blew lots of stuff into water. but it also could be mixer elbow.
does rpm vary while running? or is song steady?
the elbow can be cleaned and reinstalled to see if that is the issue. if it is not, then it will be injector pump.
if you can find phil, he cleaned his when i was there-- seemed to work well after.

[Mike Sibley]

Went out to the boat this morning to check a few things. The problem is not the transmission nor the air filter. When I started the engine this morning, it ran roughly in neutral and eventually would not run or start, even in neutral. It guess it is clear that it is a clogged mixing elbow.

After thinking about it for a minute, I wonder if water may have been forced into the engine by the blocked elbow. Is this a possibility and if so is there any way to rescue the engine.

[a64pilot]

If you think there is a possibility of water in the engine, pull the injectors and with the seacock turned off, spin the engine over, if there is water in there, you will know as it will blow out. If there is water, then spray some kind of lube like WD-40 in each cylinder and spin it over, apply WD-40, repeat. Then leave a bunch of oil in each cylinder, heck fill them up.
Fix problem and with injectors still out rotate engine by hand first to expel oil, then spin it over with the starter. Reinstall injectors and start her up, then open seacock.
I doubt there is water in there, put pulling an injector and spinning her over will tell for sure.
I have not seen an elbow clog to the point where it won't run, but that doesn't mean it couldn't.

If you are unable to do this, I'd call a mechanic ASAP just in case your right, if you act fast I do not think it will be damaged, leave salt water in there and I'm sure it will be.

Often water in an engine will hydro lock it, a Diesel has a very small compression chamber and only a little bit of water will lock one solid as water isn't compressible of course, if it's spinning over that is even more evidence to me that there isn't water in there.

But call a mechanic and be sure, if your right, you have to act fast.


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[Jason Flare]

As a64pilot said, If it's turning over it doesn't have water in the cylinders. But if it's turning over and not starting, turn off the seacock that supplies the raw water. Turn it back on if/when it starts.

You can water lock the engine cranking it without the running engine exhaust forcing out the raw water.

[tkeithlu]

The above nailed it. Black smoke from a diesel is partially burned fuel. White smoke is completely unburned fuel. Somehow you're either not getting the air necessary for full combustion to at least one cylinder or (much less likely) you're not getting the necessary compression. Check every step in the air flow, including the exhaust.

[Mike Sibley]

scHylyte, a64pilot, Neptune's Gear and Zeehag nailed it! I removed the mixing elbow today and it was clogged up with hard black grit, with only a very small opening just large enough for a small screwdriver to get through. I am totally surprised it would even come close to starting in that condition. The engine spins without spitting out water (seacock and fuel valve closed) so I am assuming that the blockage in the elbow did not back up water into the engine. Upon inspection the elbow showed a crack on the bottom, so a complete replacement is in order if I can find one.

Given that I have the elbow off, I guess it would be good to replace the hose between the elbow and muffler. Also, I should probably take the muffler out and see if it is full of gunk while I'm at it.

Thanks to all for the help! The people on Cruiser's Forum are the best!