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2004 5.0 MPI mercruiser losing power, looking for help

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  • #16
    Ok, fuel pressure 42 psi @ appx 1800 rpm. Took the boat out yesterday, added some Seafoam to the fuel, don't know when the last time injectors were cleaned. Boat ran great until I ran it full out for about 40 minutes, power loss again, then one of my passengers noticed a "popping" sound coming from the engine compartment that I couldn't hear from the drivers seat, I went back and listened, it sounded life a backfire, multiple ,pop,pop,pop , go away then pop,pop,pop again. I pulled back on the throttle a bit and it completely went away. Could not feel a miss during the popping and boat still accelerates smoothly and idles perfectly. Any ideas???
    Still need to get it to marine shop and hook up to computer. Any recommendations on a hand held unit I could use myself?

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    • #17
      The pop is the motor running lean, and the ECM should be picking up a knock and retarding timing IF the knock sensor is connected and working. In any case, did you keep the fuel pressure gauge on the motor and watch it as the rpm's increased and when it started to pop?
      94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
      95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
      07 Seadoo GTX
      Merc Adults Only VP Adults Only
      G-Dad always said "First Liar doesn't stand a chance"

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      • #18
        No, I did not keep the pressure gauge on while I was running, will have to do that next time out. Is the knock sensor on a marine engine like an automotive where it screws into a water galley on the block?

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        • #19
          Yes, it screws into a boss on the side of the block..Will have a dark blue wire attached
          94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
          95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
          07 Seadoo GTX
          Merc Adults Only VP Adults Only
          G-Dad always said "First Liar doesn't stand a chance"

          Comment


          • #20
            Ok, got bad info from son in law on fuel psi. Sorry.

            checked it myself with new OTC gauge, ignition on pump pressures up to 40 psi and shuts off. Motor running at 1800 rpm, 37 psi. Pulled vac hose off of regulator, pressure comes up to 41/42 psi. I have read about a low psi pump prior to cool fuel system, do not see one on my boat.
            serial# is om669798 if that helps. Could I install a 3/4 psi pump prior to spin on fuel filter as a booster?

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            • #21
              I meant 3 to 4 psi pump.

              Comment


              • #22
                Originally posted by Darwaypen View Post
                ...serial# is 0M669798 if that helps. ..
                Is showing up as a carburettored engine.... ????

                Chris.......
                xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                The world takes on a whole new perspective when viewed from 100’ below.
                1972 Bertram ‘Bahia Mar’ 20
                2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
                (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


                Comment


                • #23
                  Originally posted by Darwaypen View Post
                  Ok, got bad info from son in law on fuel psi. Sorry.

                  checked it myself with new OTC gauge, ignition on pump pressures up to 40 psi and shuts off. Motor running at 1800 rpm, 37 psi. Pulled vac hose off of regulator, pressure comes up to 41/42 psi. I have read about a low psi pump prior to cool fuel system, do not see one on my boat.
                  serial# is om669798 if that helps. Could I install a 3/4 psi pump prior to spin on fuel filter as a booster?
                  Sounds like the regulator is failing...

                  Found this on line https://docplayer.net/46058600-Table...ification.html Had a look, and it's a great read. Plenty of good info on the regulator and pump theory of operations.

                  Chris........
                  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                  The world takes on a whole new perspective when viewed from 100’ below.
                  1972 Bertram ‘Bahia Mar’ 20
                  2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
                  (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


                  Comment


                  • #24
                    Get it up to speed with gauge attached and let us know
                    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                    07 Seadoo GTX
                    Merc Adults Only VP Adults Only
                    G-Dad always said "First Liar doesn't stand a chance"

                    Comment


                    • #25
                      its definitely an MPI,
                      I tried posting pic of serial number badge but no luck.

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                      • #26
                        yes sir, taking it out Friday, will take fuel pressure gauge with me. thanks

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                        • #27
                          Ran with fuel pressure gauge hooked up, up to 4800 rpm pressure remained 37-38 psi. Took vac hose off of regulator, pressure comes up to about 40-41.

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                          • #28
                            Did you run it until it started loosing power or any kind of popping going on?

                            At those pressures I don't see it being the fuel pump.
                            94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                            95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                            07 Seadoo GTX
                            Merc Adults Only VP Adults Only
                            G-Dad always said "First Liar doesn't stand a chance"

                            Comment


                            • #29
                              No popping this time, but did lose its usual 1000rpm's after about 40 minutes of 4800-4900 rpm. pressure remained unchanged during the event. As usual slowed down putted around for a bit, acceleration was smooth, ran for about 15 min at the aforementioned rpm and lost power again. I can cruise all day long at 35 mph which is about 3800 rpm without issue, but that hard running brings something out in her. we've named her "Christine"

                              Comment


                              • #30
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                                Guess, going to need a scan tool on the motor when it happens to see if any codes or faults show up
                                94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                                95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                                07 Seadoo GTX
                                Merc Adults Only VP Adults Only
                                G-Dad always said "First Liar doesn't stand a chance"

                                Comment

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