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Hi All,

I have a single Yanmar 4LHA STP ,

It takes 30 to 50 sec to get up on plane with a lot of black smoke,

runs fine at top end WOT is 3400,

the injectors were bench tested and all 4 popped at 3,000 lb ,

the boost pressure at the intake manifold is low during acceleration with the gage needle bouncing from 0 to 10 psi, at 3,400 rpm under way the boost pressure is 28 to 30 psi at the intake manifold,

I power washed and had the after cooler sonic cleaned twice , i can´t see through the tubes on the air side but I think its clean because I´m getting 28 - 30 lb of boost at WOT.

the turbo fins and bearing feel tight and spin freely and look ok some carbon build up, the turbo dump valve is free and seems to be working fine,

I changed the fuel filters and the air filter,

the fuel tank and lines look clean and are free flowing and the fuel is not at all cloudy.

the bottom of the boat isn´t dirty,

The exhaust drops 14 inches from the mixing elbow and seems to be clear with a small amount of corrosion on the mixing elbow,

I have the same prop that I had before the problem, It was a gradual not an abrupt change in the slower acceleration.

It has a Yanmar fuel pump delivering 20 lb to the injector pump, I measured it after the filters,

The Yanmar injector pump has a diaphram governor with an air line running to the intake manifold being adjusted by the boost pressure witch in turn regulates the amount of fuel delivered to the injectors,

Has anyone had experience with these pumps ???????

Any help would be appreciated

Steve

Turbo blades dragging on housing reducing boost, waste gate stuck open.

If just looking at "basics" it seems you have an "overloaded" condition.

When I say overloaded it may not necessarily mean you are overwheight. I am saying the engine is not able to create the power it needs and what is could be causing it. Diesel will smoke when overloaded or if they are mechanically not running correctly. Out of proper timing etc...

You said props are good, so we can eliminate that.

Bottom clean, you can eliminate that.

Turbo not functioning correctly??? Maybe

Injector Pump malfunctioning??? Maybe

Are you 100% sure that you do not have something hung up on your prop or shaft??? Is it an inboard or I/O??? Can you VISUALLY see your prop.
I had an issue this summer when I had some crab trap twine hung up on my prop and I was smoking like I was leaving a smoke screen and labored very hard to get the boat out of its way. Once I reversed her it let loose and problem solved.

You do say that this has become a gradual problem so I would be more inclined to think it is a "mechanical" issue. I do not know how your I/pump advances its timing but that could be looked into as a possibility if it is mechanically controlled.

Boost control/waste gate (if you have one) could be looked at as Bruce mentioned

Thanks for the reply,
I think the turbo and wast gate are fine because it makes 28 to 30 lb of boost at WOT 3400 rpm, do my assumptions sound correct ?

What Bruce said!

A friend call me today to explain to me that he had the same problem with one of his Yanmars (170 hp). After changing filters, cleaning bottom, changing injectors, etc., he found that the turbo blades were skidding on the shaft when under load. Rust and wear. If the other engine is not having the same problem, switch the turbos (if possible) and rule out.

I must clarify, the engine smoked when he accelerated and continued to smoke under load.