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Slow acceleration, Black Smoke

Discussion in 'Engines' started by wetline, May 1, 2021.

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  1. wetline

    wetline New Member

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    Hi All,
    Im having trouble with my engine spooling up to slowly,

    It's a single Yanmar 4LHA STP , in a Judge Chesapeake 27

    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 with some smoke,

    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 took it to Metro Fuel shop and they said it looked fine, within spec.

    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, I think it's called an (aneroid)???

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

    Any help would be appreciated

    Thanks Steve
  2. Capt Ralph

    Capt Ralph Senior Member

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    Bad turbo.
    Bad turbo.
    Bad turbo.
    Bad air filter or air restriction???
    Naw,
    Bad turbo.
  3. wetline

    wetline New Member

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    you really think so ? after a turbo shop checked the specs and said its ok. the reason i dragged my feet is a new one is $3,000. thanks for your input.
  4. Capt Ralph

    Capt Ralph Senior Member

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    Re-read your post.
    Bad turbo.
    Unless you left something out.

    In my history, I swore a John Deere turbo felt and spun free, Lost my shirt on that job.
    Lots happens at turbine speeds that you just can not feel or see cold on a bench.

    Black smoke, Not enough air by boost or air restriction. Not low compression.

    Now maybe, maybe, maybe,, do you have a cracked exhaust manifold or riser before the turbo?
    Leaking the last and best of expanding exhaust gasses may, may cause black smoke.
    wetline likes this.
  5. Capt J

    Capt J Senior Member

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    It could be air filter and easy to remove it and try it (remote but a possibility). It points to a bad turbo as far as I know. Could be fuel as well, but I don't think so. Why not get a real Yanmar mechanic out, instead of wasting your time.
  6. Capt Ralph

    Capt Ralph Senior Member

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    This brings one last idea; Air leak after the turbo to the head.
    I recall the STPs had a robust air tube system and lots of it, but things do happen (somebody stepped on an air tube)..
    If there is an air leak, you would hear it.

    So last DYI idea; Need air pressure readings from air box ( Intake manifold before the head ) under load.
  7. MYTraveler

    MYTraveler Member

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    I don't see how the air filter or fuel could be the problem and still have it run fine at higher rpms. I wouldn't think the turbo could work fine at high rpms (or after it has spun up) but not lower rpms, but it is conceivable.
  8. Capt Fred

    Capt Fred Senior Member

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    What is most unusual is the boost bouncing between 0 and 10, I would suspect something in the aneroid feedback mechanism. Or is the dump gate opened by anything more than pressure? If so then that could be problematic.
  9. Capt Ralph

    Capt Ralph Senior Member

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    Hey now, Here are some good thoughts to chew on.
    Is there a way to watch the waste gate mechanism as the pressure is bouncing.
    Not sure if any other linkage is visible while running.
  10. wetline

    wetline New Member

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    The other things that happened were, the exhaust elbow snapped in half and blew exhaust into the engine compartment filling it with the exhaust fumes, the engine had a hard time running putting out a lot of black smoke until I figured out what happened and open the hatch, I had some wire to hold it together to make it back to port about 20 minutes of easy running . some of the foam air cleaner was sucked into the engine from the heat.

    Several years after that I backed into a rock quite hard and bent the prop shaft and slightly bending the skagg, I had it repaired at Port Niantic Marine in Ct. with a new shaft, the prop was sent out and was ok, they also installed a new exhaust from the elbow to the transom, it also was cracked.
    Thanks for your opinions
    Steve
  11. wetline

    wetline New Member

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    yes I can see the linkage of the wastegate while underway, how would I test that theory?
  12. Capt Ralph

    Capt Ralph Senior Member

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    A restricted air filter, air path or any cause for the engine NOT to get it's required amount of air per fuel delivered will result in black smoke.
    The engine may eventually make RPM.

    Turbos spin at incredible high RPMs. I don't care you you are, a persons finger can not tell if a turbo is going to spin up to speed.
    Most good feels do but not all with certainty.
    More results are a real bad turbo can certainly be felt by finger when bad. Of course, this make everybody an expert.

    If a good turbo is not getting its required amount of expanding hot exhaust gasses, it will not turn up then either. Waist gate, waits gate control as in Capt Fred's post, or an exhaust leak before turbo. This will not spin up a turbo either.

    Main line, good cylinders are not getting enough air.

    Further, an exhaust restriction (back pressure);; Rat nest.
    Boost hose blew off or damaged.
    Loose or leaking air box.
    Run-away injector.
    Last edited by a moderator: May 5, 2021
  13. Capt Ralph

    Capt Ralph Senior Member

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    Carbon ingesting brings up another book of bad things.
    Has the engine run well many hours after this ingesting?
  14. BRyachts

    BRyachts Member

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    Let me start off by saying I do NOT know that particular engine or it's fuel delivery package.

    But here's a similar problem I had on large Cat's. Slow accel, heavy smoke, would slowly spool up. Sounds similar to yours.

    Here was the cause. In the early Cat fuel management package, there were the usual multiple sensors feeding back to the ECU.
    A sensor, open to the atmosphere, was used by the ECU to compare "atmospheric" pressure to boost pressure, and control fuel to prevent smoke. The atmospheric sensors would get corroded in the humid engine room and give false readings. A quick change of the sensor and all was well.
  15. wetline

    wetline New Member

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    Ralph, It ran fine for two seasons after the carbon incident,
    then it has gradually been getting worse, at first it was only once in a while, now it's a problem every time I accelerate.
    BRyachts , my fuel system is mechanical but I could see how a bad sensor would mess things up.
    thanks
  16. wetline

    wetline New Member

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    It seems a defective waste gate would dump excessive pressure at higher RPM instead of low. No???
  17. Capt Ralph

    Capt Ralph Senior Member

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    Or dump good pressure when needed all thru the RPM band.


    "gradually been getting worse"


    Let me ask a lil more on the exhaust restriction idea;
    Tell us about your exhaust system.
    The broken riser repair?
    Any other exhaust work or thoughts on this?

    How often have you really ran this puppy up to speed and kept it there for a while these last couple of years?
    Anyway to get a pyrometer and nano-gauge on board?

    With out a real tech on site, were miles away, all we can do is scratch at a few things till something goes ouch,, or click..
    Last edited: May 2, 2021
  18. Capt J

    Capt J Senior Member

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    Is your bottom and running gear clean? Is the boat at the same weight as it's always been?
  19. wetline

    wetline New Member

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    I've run the boat at 3000 to 3200 RPM for an hour and a half with no problems, it's hard to tell when I'm underway if there's much smoke at WOT.

    When new the exhaust was fiberglassed into the transom (about a 4 foot section) with no flex coupler at the aft section, when I hit the rock it cracked , the floor was cut out to fiberglass a short flange onto the transom then a flexible boot and exhaust tube installed up to the riser, this is all new and as far as I can see inside it's clear.

    I bought a boat used and always had black soot accumulate on the back of the transom, even after a half day on the water.

    The boat is a 27 footer so i trailer it and the bottom is clean and its the same weight.
    Last edited: May 2, 2021
  20. wetline

    wetline New Member

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    I may be able to get a pyrometer to measure the exhaust temp?

    What would the nano gauge read turbo boot or exhaust ?

    I was thinking of drilling a quarter inch tap on the turbo side of boost just before the after cooler, I have a gauge on the intake manifold, that would insure the air side of the aftercooler is clear.