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CAT 3126B intermittent revs dropping

Discussion in 'Engines' started by sote2006, Aug 13, 2010.

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  1. sote2006, Aug 13, 2010
    #1
    sote2006

    sote2006 New Member

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    Aug 13, 2010
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    Location:
    mediterranean
    I have a CAT 3126B engine which most of the time works perfectly but occasionally and at seemingly random intervals, the revolutions drop back to idle speed for a couple of seconds before returning smoothly to the previously set cruising revolutions.

    On average this occurs about once an hour but may happen twice in quick succession or not at all for several hours.

    The engine has never stopped completely as a consequence.

    Has anyone had a similar problem with this kind of engine or have any suggestions as to what might be causing this behaviour?

    We have investigated the fuel supply which is the obvious first place to check but there are no problems there.

    I look forward to any suggestions
  2. K1W1, Aug 13, 2010
    #2
    K1W1

    K1W1 Senior Member

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    Hi,

    Have a look at the speed pickups in the flywheel housing, they can get bits of ring gear and rust on the probes after a while and cause some odd speed stability problems
  3. sote2006, Aug 13, 2010
    #3
    sote2006

    sote2006 New Member

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    Location:
    mediterranean
    thanks I'll check that out
  4. CatTech, Sep 28, 2010
    #4
    CatTech

    CatTech New Member

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    Sep 28, 2010
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    Location:
    south FL
    I have dealt with an issue like this before and it took a while to repair due to the intermittent occurrences of the problem.
    You did not say if this is a twin engine installation. I am guessing that this is only effecting one engine if it is. Fuel is a likely cause but easily removed from the cause by replacing both the primary filters and the on engine secondary fuel filters. You may also try swapping the fuel supply lines from port to starboard engine and vice versa to see if it is a tank/ fuel line issue. ( if this can be easily done)
    You did not mention if there are any warning or diagnostic lights coming on when this happens. CAT displays will display the error code if any are present during this loss of RPM.
    Another cause may be the controls are actually asking for this RPM and the engine is just responding to the input from the throttle control. This can only be monitored with CAT diagnostic software. This software will also be able to monitor injection actuation pressure and fuel pressure. If either of these decrease it will cause a loss of RPM.

    The suggestion of checking the speed sensors is a good one also but this is monitored very closely by the engine ECM and WILL store/ display a fault if their signals are erratic or missing.

    So basically once fuel delivery is eliminated as a problem you need a CAT tech read any stored faults or if you are lucky to capture the problem with CAT diagnostic software on a sea trial.

    Good Luck and safe boating