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Man 1050 RPM issue

Discussion in 'Engines' started by JSD82763, Aug 21, 2011.

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  1. JSD82763, Aug 21, 2011
    #1
    JSD82763

    JSD82763 New Member

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    I have a 2001 50 Viking SF with 1050 mans. The boat runs great and has just returned from its 2000 hr MAN service (gulp!) The port engine has an occational RPM drop (up to 1000 rpm) but only for a split second. It drops off and the spools right back up with a little puff of black smoke. The timeing is irreglar. It can go 10 min or 40. It seemed to resolve its self and for a couple of weeks went away but is now back. I had wrote it off as air in the fuel lines due to the major service but am biggining to re-think it as being electrical. Not sure where to look. Could it be the engine room shut down switch? Is it a turbo issue ? or loose harness? Any input would be great as the boat is in the Bahamas until next year and I dont trust the MAN agents here. Thanks for any comments.
  2. Capt J, Aug 21, 2011
    #2
    Capt J

    Capt J Senior Member

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    It sounds like air in the fuel line to me as well, however it's too tough to say. It could be in the engine throttle control. It could also be in the injector pump, boost sensor, turbo, or any myriad of things. I've seen MAN boost sensors go bad and the engines loose rpm's like that. Generally when the boost sensor goes bad, it won't spool up past around 1200 rpms.
  3. JSD82763, Aug 21, 2011
    #3
    JSD82763

    JSD82763 New Member

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    Thanks, I just did a complete inspection of the wire harness and have found what appears to be a broken "speed" sensor. The wire is still attached but the plastic housing is broken. With the ignition turned on (without the engine running) when i move the wire it is sparking. When I disconnect the sensor I get a warning light on the panel that says "speed Sensor failure. I'm hoping that when I hit a wave it was shorting causing the problem. I am going to check with the MAN people in Ft Lauderdale tomorrow and see what they think. It would be great to know that is the problem. Thanks for the feed back.
  4. Capt J, Aug 21, 2011
    #4
    Capt J

    Capt J Senior Member

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    It definately can be the problem. I would fix it and see what happens.
  5. Capt Ralph, Aug 27, 2011
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    Please let us know the results.
    ,rc
  6. Marmot, Aug 28, 2011
    #6
    Marmot

    Marmot Senior Member

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    This may have already occurred to you but any of the sensors that provide an input to the slowdown can cause that if there is a loose or corroded connector. Try removing, cleaning and replacing all the sensor connectors you can find. Some of them are difficult to locate and reach so make a note of the orientation since you will have to replace them blind.
  7. BertramGuy, Jun 9, 2012
    #7
    BertramGuy

    BertramGuy New Member

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    Bosch Injection Pumps

    It's the BOSCH Injection Pumps. Rebuild them every 2500 hours INCLUDING barrels and plungers and you will be a very happy guy.
  8. K1W1, Jun 9, 2012
    #8
    K1W1

    K1W1 Senior Member

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    Hi,

    Delivery Valves in fuel pumps are a mechanical thing, they will not be the cause of sudden changes in things that auto correct .

    Once they are worn their efficiency will drop off for sure.

    The OP's problem reads much more like a sensor/ connector problem than a worn delivery valve.

    The original post was made so long ago hopefully the OP has found the problem and he can post the answer here for the benefit of others.
  9. BertramGuy, Jun 9, 2012
    #9
    BertramGuy

    BertramGuy New Member

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    Delivery Valves

    Duly noted but I have seen a lotta work done to BOSCH injection pumps misdiagnosed and get the feeling on Man Engine there are a lot of BOSCH pumps that need this kind of work. Especially when I read about 1K fluctuations that come and go with no rhyme or reason. When these valves wear down its not just power decline but fuel/carbon on the water, especially during transition.
  10. Capt J, Jun 9, 2012
    #10
    Capt J

    Capt J Senior Member

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    How do you not trust the MAN dealers in Fort Lauderdale? There are several very good ones to choose from. They are in MAN of North America's backyard as their headquarters are in Pompano Beach.
  11. BertramGuy, Jun 9, 2012
    #11
    BertramGuy

    BertramGuy New Member

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    I just like dealing with a shop I can drive to if need be. I am in Oakdale NY and my pump guys are a 5 hour drive. That's all. Nothing against Florida. I have however heard they keep the calibration codes as a way to PUMP you up on return work. LOL
  12. Capt Ralph, Jun 9, 2012
    #12
    Capt Ralph

    Capt Ralph Senior Member

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    UH?
    I think someone moking something and not sharing?