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MTU Series 60 Won't Rev Over 1500 RPM

Discussion in 'Ocean Yacht' started by alvareza, Aug 10, 2019.

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  1. alvareza

    alvareza New Member

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    On our last trip from Scituate to Nantucket my port engine would not rev up over 1500 under load.

    This occurred the first time after running for an hour at 1800 rpm then slowing to idle to close the forward enclosure window. After running for a few minutes at 1450, stopped and started from idle, redid sync, thinking it might be a synchronization issue. Ran fine the rest of the way. Some more residue on the transom than usual at the end of the run.

    On the way home it happened after we slowed down to 900 rpm to go through the canal. About 40 minutes of slow running. Port engine would not go over 1500 with sync or using individual throttles when we got through the canal and tried to get back to fast cruise.

    Both fuel vacuum gauges were the same about 9psi at 1480 rpm. No alarms and all the temps I could think of taking with the infrared were within a degree or two.

    Any thoughts on what to check while waiting for the MTU tech to find time in their calendar?
  2. jlresq

    jlresq New Member

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    Check your fuel filters on that side.
  3. Pascal

    Pascal Senior Member

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    I always start with fuel filters, including the secondaries.

    In you cases I would also check all throttle linkages
  4. PacBlue

    PacBlue Senior Member

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    When’s the last time you had the fuel filters changed, how many hours on them now?
  5. Beau

    Beau Senior Member

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    Sounds to me like you have a sensor slowing the rpm because it "senses" something wrong, and this is a protection/get home feature. Put a computer on it.
  6. gsholz

    gsholz New Member

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    Do the MTU Series 60s have the DDEC displays? Any codes? What are the boost pressures and air intake temps at 1500 rpm under load? Any black smoke under load?
  7. Capt J

    Capt J Senior Member

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    If you're running 30 microns in the racors it's most definitely clogged secondary fuel filters. Since the switch from High sulfar offroad diesel to Low sulfar offroad diesel, I've seen on 3 different relatively new yachts have issues with the displays showing low fuel pressure, the 30 micron racors looked almost clean and the secondaries were plugged. I only run 10 micron filters in racors on everything now. I'd rather take 20 seconds at sea to change a 10 micron racor for $15 than mess around with secondaries, filling, changing, priming, etc. I'd start there.

    Were there any codes at all? If not it might not be fuel filters at all, I'd take a hard look at aftercoolers and also change them if they haven't been changed in the last 7 years or so......or the throttles themselves, could also be batteries and/or battery voltage. In your situation it's best to get a DDEC tech out with the computer.
  8. Capt Ralph

    Capt Ralph Senior Member

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    Black smoke/soot is lack of air. Air filters, air restriction, lack of boost or over fueled injectors.
    Now were not just starving for fuel but to much and it's more damaging to the engine IMO.
    I'm assuming these are the MTU Series 60s and have DDEC. Air pressure sender numbers should be somewhere in the scrolling displays.
  9. ocean50fisher

    ocean50fisher New Member

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    I’ve had this exact same problem several times with series 60s on an ocean 50. Check the black pressure sensor on the aft end of the aftercooler. It can get condensation water or debris in it which can cause the engine to derate. It comes off with two 8mm bolts. If water comes out of the aftercooler or sensor after you take it out this is almost assuredly the problem. May need to clean the aftercooler condensation drain lines too.
  10. Capt Ralph

    Capt Ralph Senior Member

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    There we go, Some real history towards what I was thinking.
    Record the pressure numbers before and after. keep all notes in an engine log.

    Go here ASAP. If there is moisture in there, it's doing more damage every day.
  11. Beau

    Beau Senior Member

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    Be nice if we heard back from the OP?
  12. alvareza

    alvareza New Member

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    Thanks for the prompt to update and the suggestions from everyone.

    The fuel filters were new in May at 1061 hours now at 1158 hours. So about 100 hours. I do have 30 micron filters on the Racors which seem clean visually. Thinking I will switch to 10 micron on the Racors. Any downside to doing so?

    Not sure how to inspect the fuel filters on the engine. My thought is to remove, pour it out into a glass jar to look at it and replace with a new filter. Waiting on new filters.

    I swapped the two air pressure/turbo boost sensors between the engines. The issue remained with the Port engine, Stbd ran over 1500 under load. I did not try getting it over 1600, since the Port engine was not matching revs. Turbo boost on the display showed 13.8 and 14 at idle both rising to 21 at 1500, Stbd went higher as it revved up, I think 23 but did not write it down. I will verify next time I run the boat.

    There was no water when I removed the sensors though both openings were moist. I rerouted the CAC drain line for the Port engine to eliminate a slight uphill run before it runs down down to connect to the exhaust tube.

    Tested the water in the drain hose for salt and it showed none. Regardless of this issue I will have CAC cleaned and tested in the fall. According to previous owner they are the new model and were cleaned with ultrasound ~400 hours ago now.

    I could not find any recent codes in the historical code section of the DDEC displays. Not a very friendly menu system, not sure I did not miss something.

    Going back to the boat today to see if there are any metrics showing for the Stbd engine that show as not available for the Port. I saw some not available metrics but was focused on air pressure and did not think to compare. I will run it again today to get air temps, double check boost pressure. Anything else I should check?

    Fuel pressure was 63-64 on both engines.

    Hope to get the MTU tech out this Friday with the computer.
  13. Capt J

    Capt J Senior Member

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    63-64 psi sounds low for fuel pressure, but I can't remember what Series 60s run at. I always run 10 micron fuel filters, they may get dirty quicker than 30s but better than secondaries getting dirty. I'd change the secondaries if you pull them off.

    Will the engine make rpm's in neutral?
  14. alvareza

    alvareza New Member

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    Yes. Used the backup controls. I don’t know how to advance the main electronic controls in neutral. I will check again next time I am on the boat.
  15. rtrafford

    rtrafford Member

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    I'm pretty sure your fuel pressure needs to be closer to 80-85. Consider inspecting the lines, fittings along the way for possible access to air on the suction side (prior to the high pressure pump). I've had issues in the past with manual transfer/primer pumps that typically failed and allowed air to be introduced to the fuel pump.
  16. Capt Ralph

    Capt Ralph Senior Member

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    IMO, your defeating the role of in-line, reducing element fuel filters.
    Stay at 30 for the mud filters and stay at 8 (stock) for the secondary filters. Remember, it's a reduction plan.
    10 & 8 is not offering you anything.
    Series 60 & 70s move fuel to cool the injectors. The fuel pressures may be lower than were used to on the DDEC 2-strokes (remember that restriction on the fuel return fitting for 2-strokes) .
    Look forward to Fridays reports from your MTU tech.
    Please keep us up..
  17. Capt J

    Capt J Senior Member

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    I have seen 3 different almost new boats with fuel pressure issues in the past few years to the point the computers were alarming. 2 different manufacturers, yachts under a year old, 1 still owned by the manufacturer and another a customer boat. All 3 had fuel pressure alarms, showed low fuel pressure on the display and on all 3, the 30 micron racors looked almost perfectly clean. All 3 of them had plugged secondaries. 2 CAT yachts and a VOLVO IPS yacht. The lower sulpher offroad diesel breaks up the algae particles into smaller particles than 30 microns and they completely bypass the 30's. CAT, MAN, and Volvo request 10 micron fuel filter elements in the primary filters (nobody enforces this from what I've seen). I sure as heck would rather spend 20 seconds changing a 10 micron filter that's dirty, then mess around with fuel and changing secondaries in a hot engine room.

    Yanmar, CAT, and most others are running a 2 micron secondary these days.
  18. PacBlue

    PacBlue Senior Member

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    Here's some info on fuel system data for a S60. Converting in. Hg and your Vacuum measurement of 9 psi seems high, 12.2 in. Hg is 6 psi maximum for a dirty system.

    upload_2019-8-15_10-1-52.png
  19. alvareza

    alvareza New Member

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    Thank you for this info. I am going to check it again and verify gauge is reading psi.
  20. PacBlue

    PacBlue Senior Member

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    It sounds as though the DDEC governor has activated Smoke Control, which means it is reducing fuel delivery. Smoke Control and Fuel Pressure do not show up as separate codes, but you can have your guys look at the engine related boost pressure issues. After talking with some knowledgeable S60 guys, lack of turbo boost can be due to the following:

    1. A damaged compressor or turbine wheel, would require replacement.
    2. The Charge Air Cooler (CAC) air fins could be contaminated. They would then need to be removed and cleaned in an ultrasonic solvent tank.
    3. The old style fiber intake manifold gasket is leaking, they should be replaced by metallic ones.
    4. The CAC gasket is leaking air, you can see if the gasket is pushed outside of the gasket surface area. If so, replace the gaskets (2).
    5. The compressor to CAC housing J-tube is leaking boost on the bottom side, usually pin hole leaks, and if so, the tube will need to be replaced.
    6. Easiest - the boost pressure sensor measuring passageway has salt build-up or has water in the sensor passageway. Clean and remove water.

    Hope it helps.

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