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Low power under load - 3988 Cummins 330

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    Low power under load - 3988 Cummins 330

    This is a new boat for me. First time out yesterday and the port engine would not get over 1500 rpm under load. Increasing throttle caused intermittent surging until it eventually slowed and stopped on it's own. Starboard engine is fine. Port engine runs up easily with no load. There was no smoke under load when the problem occurred.

    I replaced the main Racor and checked the throttle linkage for full range. Started at the dock and all seems well with no load. The fuel solenoid appears to be fully engaged when it was running.

    The sea trial was about 6 weeks ago and everything checked out. The only change I made was to set the fuel valves for port feed and return to port engine and starboard return and feed for starboard engine. They were different (crossed?) before but I didn't record the previous positions.

    Any ideas on other things to check before I go out again?


    #2
    Don't forget the on engine fuel filter on the port side of each engine just aft of the injector pump. They are us usually 10 microns and often overlooked.
    "Adios Dinero"
    1997 3988 with new 330 Cummins
    Photo Credit: Whiskywizard

    Comment


      #3
      Is the turbo spinning? Take off the air filter and try to spin it by hand.
      "Impasse". 2001 3988
      Cummins 330's
      Puget Sound

      "You don't want to be the richest guy in the nursing home..."

      Comment


        #4
        If everything was fine at sea trial just a couple of weeks ago and not now something changed.

        This is going to sound silly but how quickly did you advance the throttles?

        Again, I know this sounds silly but it is a brand new boat to you.

        I had a 3488 with 330’s that I bought in 2003. My FIRST time in the boat post sale, I was heading to Alaska, got out of Ballard Locks and tromped it.

        Had basically the same problem. I was most unhappy.

        Came back to idle, advanced the throttles slowly, and the boat ran fine for my 1500 mile long trip.

        KEVIN SANDERS
        4788 LISAS WAY - SEWARD ALASKA
        where are we right now​​​​​​???​

        https://share.findmespot.com/shared/...j23OquWOj2N3Xe

        Comment


          #5
          Thanks for all the responses. I will replace the engine fuel filter and check the turbo. I did advance the throttles slowly.

          One more piece of info, I had about a 40 minute run at near idle, before asking her for more power.

          Comment


            #6
            Originally posted by Renilyab View Post
            This is a new boat for me. First time out yesterday and the port engine would not get over 1500 rpm under load. Increasing throttle caused intermittent surging until it eventually slowed and stopped on it's own. Starboard engine is fine. Port engine runs up easily with no load. There was no smoke under load when the problem occurred.

            I replaced the main Racor and checked the throttle linkage for full range. Started at the dock and all seems well with no load. The fuel solenoid appears to be fully engaged when it was running.

            The sea trial was about 6 weeks ago and everything checked out. The only change I made was to set the fuel valves for port feed and return to port engine and starboard return and feed for starboard engine. They were different (crossed?) before but I didn't record the previous positions.

            Any ideas on other things to check before I go out again?

            "This is a new boat for me. First time out yesterday and the port engine would not get over 1500 rpm under load. Increasing throttle caused intermittent surging until it eventually slowed and stopped on it's own. Starboard engine is fine. Port engine runs up easily with no load. There was no smoke under load when the problem occurred."

            Is this a correct summary?
            - Boat ran good 6 weeks back
            - now pt engine loses power at 1500 rpm
            - no smoke when losing power
            - surging prior to stall
            - runs with no load
            - only pt engine stb is fine

            This is most likely a fuel problem to the pt engine …
            - with the boat 'off' have someone advance the throttles to full and make sure the pt engine fuel lever fully reaches the stops
            - are the tachs known accurate?
            - check the fuel tank level delivering to the pt engine (not just the gage)
            - check for 'pinched' or cut flexible fuel lines leading to the engine
            - check all filters for blockages and air leaks
            - check water filters for blockages and leaks
            - check the air vent on the tank delivering the pt engines fuel (van temporarily leave the fuel cap off as long as not risk of water getting in there)

            Last resort bypass the fuel manifold and make sure the pt engine is receiving full fuel load at the fuel pump.
            Northport NY

            Comment


              #7
              I wonder if there is a reason the fuel valves were set differently at sea trial.


              KEVIN SANDERS
              4788 LISAS WAY - SEWARD ALASKA
              where are we right now​​​​​​???​

              https://share.findmespot.com/shared/...j23OquWOj2N3Xe

              Comment


                #8
                Originally posted by ksanders View Post
                I wonder if there is a reason the fuel valves were set differently at sea trial.
                Maybe low fuel on one tank.
                Northport NY

                Comment


                  #9
                  Originally posted by smitty477 View Post

                  Maybe low fuel on one tank.
                  Or maybe a known problem with fuel supply?

                  KEVIN SANDERS
                  4788 LISAS WAY - SEWARD ALASKA
                  where are we right now​​​​​​???​

                  https://share.findmespot.com/shared/...j23OquWOj2N3Xe

                  Comment


                    #10
                    After replacing the on engine fuel filter and rechecking the throttle linkage and fuel solenoid I went out for more tests.

                    Initially there was no improvement, so I experimented with fuel valve settings. Bottom line, the port engine does not like to be sourced from the port tank.

                    Sourcing the port engine from the starboard tank gives me full port engine power. Sourcing the starboard engine from either tank also gives full starboard engine power. As long as the port engine is sourced from the starboard tank I get full power with return in either position.

                    I think all this tells me the fuel and engine is good. I believe I have the problem narrowed down to one line and/or one valve.

                    Comment


                      #11
                      Originally posted by Renilyab View Post
                      After replacing the on engine fuel filter and rechecking the throttle linkage and fuel solenoid I went out for more tests.

                      Initially there was no improvement, so I experimented with fuel valve settings. Bottom line, the port engine does not like to be sourced from the port tank.

                      Sourcing the port engine from the starboard tank gives me full port engine power. Sourcing the starboard engine from either tank also gives full starboard engine power. As long as the port engine is sourced from the starboard tank I get full power with return in either position.

                      I think all this tells me the fuel and engine is good. I believe I have the problem narrowed down to one line and/or one valve.
                      Good troubleshooting!

                      KEVIN SANDERS
                      4788 LISAS WAY - SEWARD ALASKA
                      where are we right now​​​​​​???​

                      https://share.findmespot.com/shared/...j23OquWOj2N3Xe

                      Comment


                        #12
                        Clogged pickup tube in port tank.
                        "Adios Dinero"
                        1997 3988 with new 330 Cummins
                        Photo Credit: Whiskywizard

                        Comment


                          #13
                          Originally posted by The_Other_Gary View Post
                          Clogged pickup tube in port tank.
                          He says the starboard engine runs fine from the port tank so it's not likely the pickup tube but might be a line itself or a valve.
                          Future 4788 Owner
                          Charleston, S.C.

                          Comment


                            #14
                            They are 3 different pickup tubes in each tank, one for each engine and one for the generator. This may also dictate a good tank cleaning is needed.
                            "Adios Dinero"
                            1997 3988 with new 330 Cummins
                            Photo Credit: Whiskywizard

                            Comment


                              #15
                              Do the 39's have screens on the pickup tubes? Should be an easy fix with any luck.

                              James
                              1989 Bayliner 3888, 175 Hinos,
                              Hurth 630's Onan 8kw MDKD
                              Lowrance Electronics!
                              Boating on Georgian Bay & the North Channel
                              Completed the Great Loop 07/25/19
                              AGLCA #8340
                              MTOA# 7469

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