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OX66 sudden Loss of power then regain

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  • OX66 sudden Loss of power then regain

    Hello all,
    I have a 2002 OX66 250 HP Saltwater series 2 stroke. Lately its been giving me a little issue, when I'm running on a flat day it runs like a champ with no issues. However if I hit some rough seas, when the nose goes up high enough power will almost completely cut off then as the nose returns down (level) again, power completely restores itself and runs normal again. For example, I was running the boat yesterday at 4200 RPMS and hit some waves, when the nose went up the RPMs dropped to 2100 RPMS the restored back to 4200 RPMs when the nose dropped again.

    Any ideas?

    Thanks in advance.

  • #2
    VST filter clog is usually the culprit with your description.


    • #3
      ill second the vst issue.


      • #4
        Thank you gents. I'll get it cleaned out and let you know what happens.


        • #5
          ok, so I replaced the VST filter with a new one. The old one was brown and had some particles in it so I figured a new one would be best. I took it out for a spin today and at first she ran like a champ.

          New Problem: Generally, if I run open throttle itll go about 50, 51 or 52 RPMs which is ok for me. gives it enough speed that im happy with. Now prior to replacing the VST filter yesterday, it did what im about to describe once or twice in the past but today it was way more constant.

          So once I get up on plane doing about 45 RPMs (not full throttle), it will slowly on its own start dropping 44, 43 ,42 then stay at about 41. if I open her up full throttle not much happens, it may go up an RPM or two but then go back down. The most I was able to get was 45 RPMs, which kinda sucks.

          Now recently I replaced the fuel filter on the port side of the engine, the filter in the water separator and yester the VST filter. so Im pretty sure its not any of those causing the issue. I've never replaced the high or low fuel pump diaphragms, could that be the cause?

          Hope someone can help. Thanks


          • #6

            replace your lift pumps ( no matter what) and install a clear section of fuel line and a T for a vacuum guage...nothing above 3 kpg is acceptable..and/or ck fuel pressure off the "scharder" valve....


            • #7
              what is the fuel rail pressure when its running poor?


              • #8
                i'm assuming that the lift pumps are another way of referring to the HP and LP fuel pumps. Ive never replaced them and I'm fairly certain the previous owner never did either. Is the work fairly easy to perform? it doesn't look difficult but id appreciate any instruction you may have. I also noticed on the diagrams that each one has two gaskets and two diaphragms on each pump which is more costly than buying the entire pump assembly (makes no sense). haven't checked the pressure under load but last time we checked the pressure it was good. also hooked up the tester to the engine and it has no errors. I haven't, but will, install a five gallon take to the engine and see if it still does it.


                • #9
                  your motor has three low pressure lift pumps.
                  it has one high pressure pump.
                  typically you have to loosen the VST to acess them.


                  • #10
                    ok so remove VST and replace them. the low and high pressure pumps are all the same correct?


                    • #11
                      nope the high pressure pump is in the VST and cost a lot more than the 3 lift pumps together.

                      Sometime buying the complete lift pump means saving money over buying all the parts


                      • #12
                        The 3 low pressure pumps are the ones to replace. HP pump either works or doesn't. If it doesn't work, the motor won't run.


                        • #13
                          thank you gents. I've ordered all three pumps and will let you know how it goes once they're installed. Thank you all for your comments, very helpful.

                          I also ordered Ringfree which im told is really good in clearing deposits. Anything I need to know about that or just dump in the tank and go?


                          • #14
                            read the lable and follow the instructions .
                            small amount for everyday fuel use.

                            There is a shock treatment of adding more to help clean things up at 1st if motor has a lot of carbon


                            • #15
                              Originally posted by Gill7858 View Post

                              I also ordered Ringfree which im told is really good in clearing deposits. Anything I need to know about that or just dump in the tank and go?
                              +1 ^^^

                              Its like 1 oz per 10 gallons for reg operation. I run it in every gas engine I own. You can easily run it 2x the amount W/O hurting anything. I use it regularly(in the boat too)..

                              Heck it cleaned up the injectors in my Four Runner and brought an occasional high idle back down to normal.., Really, really good stuff...
                              1997 Angler 204 CC, 2006 F150 TXR