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2003 RX DI Limited RPM

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  • 2003 RX DI Limited RPM


    Here is the thing:

    Its a 2003 RX DI which doesn't go above 4850 rpm. Normal acceleration, normal idle, normal everything.

    Fuel and air injectors cleaned, new seals and filters.
    Fuel pressure at 107 psi. Not tested when on water, but the rpm behaves the same all the time doesn't matter if in the water or out.

    Reeds are fine and rave valves too. Both checked and cleaned. Also checked and replaced all o rings for the air line. But as fuel pressure is good, I assume that's not an issue.

    I don't have CanDoo yet, but is there anything in the ski that would limit the engine to 4850 rpm? I can not confirm that I have a learner key, but I think the ski is limited in speed not in rpm.

    When i reach 4850rpm and give more throttle, the engine just starts to make a different sound like a deeper humming/knocking.

    No maintenance light or fault code present too.

  • #2
    Close-up pic of both spark plugs please. Are you SURE the reeds are all good? Did you inspect the tubing that runs the RAVE system? Last thing I can think of is a bad MPEM.


    • #3
      The RAVE's and the reeds are 100% good.
      I removed both reeds and checked them. They seal good and looking fresh.

      Rave are disassembled and cleaned. Also I moved them by just blowing in the tube. Also checked their movement (2x clicking) when turning of the engine.

      Spark plugs ran 10min on the hose total, and 30min on the lake.
      I hope the oil fouling is coming from the oil in the crank case. Ski stand for a year or so. Fuel was drained before first crank, and i checked the pistons for any corrosion before the first crank.

      Click image for larger version

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      Attached Files


      • #4
        I thought about the spark plugs. The oil pump will be fully open at wot, ans will inject too much oil for too low rpm.
        I will check the compression tomorrow and also but new plugs in ans only run it up to 4000rpm on the hose to see how they look.


        • #5
          Compression is low, top end is done and need a rebuild.


          • #6
            Well........DAMN! How many hours? The 951 is only known to run arojund 150 hours before needing a top end. I've only ever seen one that went over 200 hours.


            • #7
              So here is the thing, it has 220h on it, but the engine is looking decent from the outside.
              Pistons rods have needle bearings without a cage. So either it's the first motor, or it was an OEM rebuild that went in. But I don't know anybody using needle bearings without a cage. Luckily I was prepared when I removed the pistons.

              Crankshaft is in very good shape.... luckily.

              Anyhow lines up with approx 100h.

              the oil pump is fine, and also the injection nipples. Injectors looked very bad before I send them for cleaning. Not sure what caused it yet, maybe fatigue. One piston rings was completely gone, the other piston had one that was broken as well and came apart in two pieces when I pulled the top end.

              Also the drain hose from the top end bottom part to the pump was clogged with sand. But should just have prevented water to leave the engine, not clogging waterflow.
              Attached Files


              • #8
                That ring snagged the exhaust port. I'm betting the piston to cylinder clearance is WAAYYY out of spec........like 15 thousandth or more.


                • #9
                  So thanks to a nice company starting with an S. and ending with an T. The top end is overhauledz which is good.
                  What is a bummer: rpm issue is the same....

                  If nobody has an idea I will check the fuel pressure with a new gauge. If thisI will be okay i think I will tackle the MPEM....


                  • #10
                    Fuel pressure tested good! During idle I have fluctuations around 107psi. When giving throttle its stable.

                    is it worth to put the next stack of money into it and buy candoo pro, to Mayne reset the tps? Any other ideas?

                    Also replaced the ignition coils and the cables plus plugs.


                    • #11
                      Really sounds like you might have an MPEM issue. Have you checked voltage while running? Get it hooked up on the hose, start it up and let it warm a bit. Put a meter on the battery and watch voltage. slowly rev it up to the point it won't rev any more and let me know what the voltage does.


                      • #12
                        Here you go:

                        Looks stable to me!
                        before I rip our the mpem, is there a likelyhood the tps is causing it? Wrong calibration or offset?

                        Also I removed the exhaust to check if there is any restrictions. Without success. Compression after the rebuild is 97 psi on both cylinders. I hope this is due to the rings not yet seated / breaked in.


                        • #13
                          Yep, voltage looks good. If you have a cheapy compression gauge that's probably why it's only reading 97psi. Check this out...A word about compression testers - Greenhulk Personal Watercraft Performance Forums
                          Good compression on 951 engines is around 120psi.
                          Check with Westside Powersports, they might be able to test that MPEM. I had a GTX here last year with MPEM issues and I believe it was also RPM limited.....it's just one of the failure modes I guess.​


                          • #14
                            I can confirm, it was the mpem! What a pain!

                            Thank you very much guys, you rock!!!!


                            • #15
                              Glad you got it figured out.