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8V92Ti black smoke under load

Discussion in 'Engines' started by Capt Burt, Sep 5, 2021.

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  1. Capt Burt, Sep 5, 2021
    #1
    Capt Burt

    Capt Burt New Member

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    Detroit 8V92Turbos J&T
    Engines rev to 2,000RPM NO PROBLEM, at slip=No smoke. But, underway black smoke??
    Prop wash shows one engine doing most of the work.
    I can get to 1/2 throttle, then no more RPM even though pushing throttles to max.
    I have:
    -Replaced fuels filters (to 20Micron)
    -Recharged/ Cleaned air filters
    -Purged Hyuantic lines
    -Added 80gal new fuel & 1 gal SeaFoam
    -Removed valave covers & checked for stuck injectors, purged/cleaned fuel lines.
    -Cleaned props.

    I am NO mechanic, but can generally fake my way around most little problems.
    Any input / suggestions would be deeply appriciated.
  2. RER, Sep 5, 2021
    #2
    RER

    RER Senior Member

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    Bad turbo
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  3. captainwjm, Sep 5, 2021
    #3
    captainwjm

    captainwjm Senior member

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    Bottom and props clean?
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  4. Capt Burt, Sep 5, 2021
    #4
    Capt Burt

    Capt Burt New Member

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    Yes sir..
  5. Capt Burt, Sep 5, 2021
    #5
    Capt Burt

    Capt Burt New Member

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    Will ck that out. Thanks much!!
  6. Capt Fred, Sep 5, 2021
    #6
    Capt Fred

    Capt Fred Senior Member

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    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.
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  7. MYTraveler, Sep 5, 2021
    #7
    MYTraveler

    MYTraveler Member

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    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.
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  8. Capt Ralph, Sep 5, 2021
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    When did this problem start?
    Overnight or thru the years?
    Any history?
    Black Smoke = Not Enough Air..
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  9. rtrafford, Sep 5, 2021
    #9
    rtrafford

    rtrafford Senior Member

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    Yes. Turbo, cooler....something either not producing or obstructing ramped up air requirements.
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  10. Capt Ralph, Sep 5, 2021
    #10
    Capt Ralph

    Capt Ralph Senior Member

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    Oh, Ensure shut down flapper is all open.
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  11. Capt Burt, Sep 5, 2021
    #11
    Capt Burt

    Capt Burt New Member

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    Shut down flapper is open. Problem started several months ago, but only 20hrs ago or so. It's a live aboard that doesn't go out very often.
  12. Capt Ralph, Sep 5, 2021
    #12
    Capt Ralph

    Capt Ralph Senior Member

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    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???
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  13. ArielM, Sep 7, 2021
    #13
    ArielM

    ArielM Senior Member

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    The no load on those engines is 2350 iirc. 2000 is quite a bit low. check turbos or after coolers.
  14. retiredguy, Sep 21, 2021
    #14
    retiredguy

    retiredguy Member

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    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?
  15. Capt Ralph, Oct 12, 2021
    #15
    Capt Ralph

    Capt Ralph Senior Member

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    Update?
  16. Capt Burt, Oct 13, 2021
    #16
    Capt Burt

    Capt Burt New Member

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    Hey Capt Ralph...Verdict still not in. Actually I currently have the aftercoolers torn down, cleaned & ready to go back together..Ill know more after reinstall.
    Thanks...
  17. Capt J, Oct 13, 2021
    #17
    Capt J

    Capt J Senior Member

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    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.
  18. Capt Ralph, Oct 13, 2021
    #18
    Capt Ralph

    Capt Ralph Senior Member

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    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.
  19. Capt Burt, Oct 14, 2021
    #19
    Capt Burt

    Capt Burt New Member

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    No, i haven't though of those. Good idea!!
    I'll try it..
    Thank you
  20. Capt J, Oct 14, 2021
    #20
    Capt J

    Capt J Senior Member

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    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.
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