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2000 21V | 5.7 Mag MPI SKI - Engine Issue??

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    2000 21V | 5.7 Mag MPI SKI - Engine Issue??

    Hey guys,

    Thought I would offer this one up to the forum. Let me know your thoughts.

    Year 2000
    2100 V Limited (essentially the 21V, but with different trim and finish)

    5.7 Mercruiser Mag Mpi Ski with aprx. 600 hours.

    She has been a FANTASTIC boat and engine for the past 5 years, then at the end of last season, we ran into an issue.

    We put in, and buzzed around the lake for 30 minutes. Then, parked and swam and ate (engine off) for 30-45 minutes. Went to start engine, and engine would turn over, but did not fire. After 4-6 attempts, the engine did started. Upon driving out of the swim spot the engine would not go above 3000 rpms, and was bogging down, coughing, and back firing all the way back to the boat ramp. (Engine died if I went too low on rpms.)

    I have been able to replicate this same issue each time out after.

    It seems to be tied to the engine getting hot. The issue of the engine not wanting to restart—and then bogging and dying—only happens after the engine has ran for 45 minutes to 1.5hrs and is hot.

    Things I have done:
    • replaced ignition coil
    • replaced spark plugs
    • replaced distributor cap and rotor
    • replaced IAC valve
    • replaced thermostat
    • replaced impeller
    • replaced fuel pump
    • cleaned fuel lines (from filter to pump)
    • replaced fuel filter
    • replaced fuel lines from tank to fuel filter

    I initially thought it was vapor lock, but the fuel pressure is good all around. Also, this 5.7s has the "cool fuel" system which runs the fuel through a pipe with water rushing through it to keep the fuel from getting too hot.

    I also did multiple compression tests at different points, cold, hot, after the issue happened. And, each compression test was within the range. (145-160s across the board)

    My hypothesis as of now:
    • slightly faulty head gasket
      • When we first got the boat 5 years ago, it overheated on our 2nd time out. I later found impeller bits in the water tubing downstream of the impeller. "Thanks previous owner..." (I now replace the impeller every other season just to be safe.)
      • This overheating lasted all of 3 seconds and I pulled the boat down to idle to get back home.
      • I am wondering if this overheating issue affected the head gasket then, and it is now beginning to failing when the engine gets hot???
    • Could this be some electrical thing when the engine gets hot?
    The frustrating thing is the engine runs like a scalded dog for 30-45 minutes. All the power you want. Smooth. Sounds good. Then... if we turn the engine off, and attempt to restart, it bogs, coughs, and eventually dies.

    OK, that is all I have... Any thoughts you may have would be much appreciated.

    Thank you in advance!

    #2
    Have you changed the pickup in the distributor? what do you mean when you say it runs fine till it gets hot? Is it overheating or normal temp hot then runs bad? coughing back through the intake is usually spark/timing related.if you haven't done the pickup do that for sure. I would check the base timing also. this is if you say it is not overheating just runs bad at normal temp hot. MAP sensor also.

    Comment


      #3
      Perhaps the cool fuel heat exchanger has a small crack in it that allows small amounts of water into the fuel line once the engine is shut off. The fuel pressure would keep the water out when running, then once you turn it off, the water in the exchanger can leak in.


      Sent from my iPhone using Tapatalk
      Last edited by USWaker; 06-16-2022, 04:30 AM.

      Comment


        #4
        Not quite 45 minutes of running, but my problem was would warm up then start lugging and surging after about 15 minutes and die at idle then wouldn’t restart. It was the coolant temp sensor. The sensor, not the sender, changes the ratio when it “thinks” the engine is cool. Easy fix to try. I replaced that and the distributor cap and rotor and it ran flawlessly all this past weekend.
        Chris

        Comment


          #5
          I guess I will try to list out the over 500 hour bullet proof that you might want to do or not. but there are 3 post here all with the same symptoms.

          1 The pickup in the distributor needs to be updated to the 3 wire. (First thing)
          2 Coolant temp sensor/ can't hurt to change the thermostat (I still haven't done this thermostat)
          3 MAP sensor
          4 IAC valve
          5 TPS sensor
          6 Of corse cap, rotor plugs (most of you have done this)
          7 new starter and alternator or Have them rebuilt.
          8 check the base timing If you know a shop that has a data com can't hurt to have them check your work.
          9 was not needed but put a fuel pump on. ( now I have a spare)
          1-6 are not that expensive parts and can be preformed in a few hours. hope this keeps you on the lake and not on the shore pulling your hair out wishing you were in the lake.

          Comment


            #6
            BLUF: Merc 350 starts, runs for ~10min, then stalls & will not restart for ~30min. Owner seeks troubleshooting suggestions. Chasing an issue on a Mercruiser 350 inboard motor. Starts up fine, idles smooth, runs at speed and under load (e.g. pulling a wakeboarder or skier), then if speed is reduced or brought back to idle

            Comment


              #7
              we had those same issues with our 2300v... we did everything you did but did not fix it... we also found what some called a "cam position sensor" that the rotor moves through under the rotor... changed that out and have had no issues since... it was corroded and would sometimes work, sometimes not...

              Rick

              Comment


                #8
                Sensor.PNG It is part number 11 in this diagram.... sensor

                Comment


                  #9
                  #11 is the pickup there is a updated version 3 wire. replace that for sure. thank you rt2439

                  Comment


                    #10
                    I guess I will try to list out the over 500 hour bullet proof that you might want to do or not. but there are 3 post here all with the same symptoms.

                    1 The pickup in the distributor needs to be updated to the 3 wire. (First thing)
                    2 Coolant temp sensor/ can't hurt to change the thermostat (I still haven't done this thermostat)
                    3 MAP sensor
                    4 IAC valve
                    5 TPS sensor
                    6 Of corse cap, rotor plugs (most of you have done this)
                    7 new starter and alternator or Have them rebuilt.
                    8 check the base timing If you know a shop that has a data com can't hurt to have them check your work.
                    9 was not needed but put a fuel pump on. ( now I have a spare)
                    1-6 are not that expensive parts and can be preformed in a few hours. hope this keeps you on the lake and not on the shore pulling your hair out wishing you were in the lake.

                    Comment

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