8V92Ti black smoke under load

Bottom and props clean?

Without any more info or history, the turbo is the best guess. If turbos spin freely and tight bearing then intercooler would be another possibility. Measuring the turbo boost is not that difficult and would provide more info for accurate diagnosis.

Could be bad injectors, as the presence of black smoke can only be explained by incompletely burned fuel. Unlikely that one bad injector would create your symptoms, so it would have to be multiple bad injectors. But unlikely that you would have multiple failures at the same time unless you have bad fuel (and filters) on a separate tank for the affected engine. Still, I would check the turbos first.

When did this problem start?
Overnight or thru the years?
Any history?
Black Smoke = Not Enough Air..

Yes. Turbo, cooler....something either not producing or obstructing ramped up air requirements.

Oh, Ensure shut down flapper is all open.

Check air hose and clamps between turbo, inter-cooler & blower. Take air filters off.
Check turbo for cracks and air leaks.
As I expressed on another thread, Even if it feels good by finger, turbos may still not spin up.
Could really use some air pressure readings on top of the blowers. Better to have air box readings also.

Whole bottom clean???

The no load on those engines is 2350 iirc. 2000 is quite a bit low. check turbos or after coolers.

Was wondering what you found? I am looking at a boat (68 foot 83000 lbs) with two of the same engines. Been advised to stay away from a boat with them as J&T really pushed hard to get the rated 735 H.P. so they wear out quickly and tend to be fuel hogs even at lower RPM cruising. Can I ask how many hours since the last major? Any other issues with yours?

Update?

Have you considered doing a compression check.....or easier still, start the motor and shoot the temperatures of each exhaust port of the exhaust manifold.

I think more of lack of air or boost per fuel (rich), than low compression.
Maybe, your thinking an over fueling injector or two.

I was just thinking if this has the TA fuel modulator, stuck or over fueling.
Starting to see more turbo issues on dock queens lately.

I've had 2 8v92's and 1 12v71 that blew tons of black smoke under load and all of them had a low cylinder......like 90 psi...... I've had dirty air filters cause it once, and turbos on a few boats also and dirty fuel filters or bad injectors on also. Being the boat sits and is so neglected by not being used, I'm willing to bet a dead cylinder. Which was the case with the 2 8v92's and they had 375 hours on them.