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F225 TXRC bogging down - fuel rail pressure question

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  • F225 TXRC bogging down - fuel rail pressure question

    2004 F225TXRC on a Parker 25SE. The motor starts easily and idles nicely. However for the past few months, the motor has been bogging down when I try to accelerate to high speed to the point where I can barely get on plane at around 4200 RPM. The motor then begins to fade out, or wants to die out until you chop the throttle and return to idle speed, at which point, the motor idles fine. To attempt to troubleshoot this issue, I obtained a fuel pressure gauge to read fuel rail pressure, as this technique has been discussed on this forum many times. So today, at key on/engine off, rail pressure was 46 psi then dropped off to 40 psi after about 15 seconds. At idle of about 1100 RPM, rail pressure was 42 psi. At 4200 RPM, the rail pressure was reading between 48-50 psi. I was able to make it to and maintain 5300 RPM where the rail pressure maintained its reading of around 48-50 psi. The boat was still slightly sluggish but not as bad as earlier this year. Honestly, I suspected an issue with my HP pump filter in the VST so I was expecting below-normal rail pressures to be indicated. However, the pressures of 48 to 50 psi seem excessively high. Does anyone know if these rail pressures are 'normal'? Thanks!

  • #2
    The high pressure fuel pump pressure at key on should be measured within 5 seconds. Reason being is that the pump only runs for about this amount of time.

    Specified pressure at key on is 42 psi. At idle RPM the fuel pressure reference value is 37 psi. As the throttle is opened up the fuel pressure will rise until it gets near, but not at, 42 psi.

    Your pressure values seem on the high side. Is the gauge new or known to be accurate?

    What I would try is to have someone mist some gasoline into the air intake system at the time the motor starts to bog down. If it picks up and runs that indicates a lack of fuel. Problem could be the injector filters are clogged. If so, you will have fuel pressure to the injectors but insufficient fuel can get through the injector filters into the intake manifold.

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    • #3
      If the pressure gauge is correct/accurate, I would think the pressure regulator could cause it also, and too much fuel is bad for proper combustion just like too little what do the plugs look like?

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      • #4
        last thing I would suspect with those symtoms is a regulator.
        I would suspect a VST filter or an injector filter or both.
        the HP filter on that motor is about the size of a pencil eraser.

        Comment


        • #5
          Originally posted by boscoe99 View Post
          The high pressure fuel pump pressure at key on should be measured within 5 seconds. Reason being is that the pump only runs for about this amount of time.

          Specified pressure at key on is 42 psi. At idle RPM the fuel pressure reference value is 37 psi. As the throttle is opened up the fuel pressure will rise until it gets near, but not at, 42 psi.

          Your pressure values seem on the high side. Is the gauge new or known to be accurate?

          What I would try is to have someone mist some gasoline into the air intake system at the time the motor starts to bog down. If it picks up and runs that indicates a lack of fuel. Problem could be the injector filters are clogged. If so, you will have fuel pressure to the injectors but insufficient fuel can get through the injector filters into the intake manifold.
          Thanks boscoe. Great point: the gauge is brand new and, in comparison to your pressure values, seems to be reading consistently high at about +4 to +6 psi. (I will figure out if the gauge is accurate. That is, I need to test the test equipment.) If I assume the gauge is inaccurate and reading high, then rail pressure is likely sufficient and points to clogged injectors/injector filters. Thanks again.

          Comment


          • #6
            Originally posted by 99yam40 View Post
            If the pressure gauge is correct/accurate, I would think the pressure regulator could cause it also, and too much fuel is bad for proper combustion just like too little what do the plugs look like?
            Thanks 99. I plan to pull the plugs tomorrow and see what they look like. IF the pressure gauge is accurate, then the rail pressure is ~48 psi from about 2500 RPM up to 4200 RPM. I'm not sure, though, if 48 psi is too much to cause an issue (an improper fuel/air ratio that bogs the engine down). Thanks again.

            Comment


            • #7
              Originally posted by rodbolt17 View Post
              last thing I would suspect with those symtoms is a regulator.
              I would suspect a VST filter or an injector filter or both.
              the HP filter on that motor is about the size of a pencil eraser.
              Thanks rodbolt. Agree, it looks like it is time to pull the injectors and VST filter, I just wasn't sure about the pressure regulator.

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              • #8
                Originally posted by Crazy Train View Post
                Thanks 99. I plan to pull the plugs tomorrow and see what they look like. IF the pressure gauge is accurate, then the rail pressure is ~48 psi from about 2500 RPM up to 4200 RPM. I'm not sure, though, if 48 psi is too much to cause an issue (an improper fuel/air ratio that bogs the engine down). Thanks again.
                Rodbolt already said he does not see the regulator being a problem, I was just guessing it might be

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                • #9
                  anyone ever wonder what that vacuum line on the regulator is there for?
                  at 48 PSI under a decent load I would not look at it anymore and move along.

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                  • #10
                    Originally posted by rodbolt17 View Post
                    anyone ever wonder what that vacuum line on the regulator is there for?
                    at 48 PSI under a decent load I would not look at it anymore and move along.
                    Given Yamaha's lack of theory of operation, anyone that wonders won't find it in a Yamaha service manual.

                    If you look at some older Yamaha service manuals there is a bit of "how it works" information. YMIS, carburetors, trim/tilt systems, CDI's, etc.. Have you ever wondered why Yamaha stopped providing that type of information? Were folks simply not reading it?

                    For those that do wonder, here is some verbiage to think about. Particularly the part that is italicized.

                    Basic Operation

                    EFI fuel pressure regulators come in various shapes and sizes but their purpose is the same- to hold the fuel pressure at a certain differential above the intake manifold pressure.

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                    • #11
                      Found this on the innerweb for 26 bucks. If I own an EFI model again I would install one just for the hellavit.

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                      • #12
                        Originally posted by Crazy Train View Post
                        Thanks boscoe. Great point: the gauge is brand new and, in comparison to your pressure values, seems to be reading consistently high at about +4 to +6 psi. (I will figure out if the gauge is accurate. That is, I need to test the test equipment.) If I assume the gauge is inaccurate and reading high, then rail pressure is likely sufficient and points to clogged injectors/injector filters. Thanks again.
                        boscoe: Using the front tire on my truck, I assessed the accuracy of my fuel pressure gauge by comparing its' reading to 4 other dial/digital pressure gauges. I also pressurized the fuel gauge with a Mityvac hand pump that has its' own gauge. Overall, taking the average, the fuel pressure gauge looks to be reading about 1 to 2 psi high. Additionally, I rechecked the 'key on/engine off' fuel pressure on the engine today: about 2 seconds after 'key on' the pressure rises from 0 to 46 psi (44 psi corrected); you can hear the HP pump working. After the HP pump shuts off, the pressure starts to drop off to about 42 psi (40 psi corrected) after about 5 seconds. Overall, I think I have adequate fuel rail pressure and will head down the path suggested by Rodbolt of the HP pump filter and/or the fuel injectors.

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                        • #13
                          Originally posted by 99yam40 View Post
                          If the pressure gauge is correct/accurate, I would think the pressure regulator could cause it also, and too much fuel is bad for proper combustion just like too little what do the plugs look like?
                          99: I pulled the plugs today. I still need to figure out how to post photos to this site, but in the meantime: all six plugs show consistent, normal greyish combustion appearance - no stand outs. All plugs still gapped at .044. Thanks!

                          Comment


                          • #14
                            myself I would test the rail pressure at the RPM and LOAD when it fails.
                            otherwise the test is a teat on a boar hog.
                            that vacuum sense line on the regulator allows for about 5PSI more rail pressure at or near WOT or when rapidly accelerating.

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                            • #15
                              Originally posted by rodbolt17 View Post
                              anyone ever wonder what that vacuum line on the regulator is there for?
                              at 48 PSI under a decent load I would not look at it anymore and move along.
                              I think boscoe answered it, but I was guessing that the regulator maintains a certain pressure but that pressure is augmented/changed by the vacuum line. I believe I read somewhere where the vacuum only comes into significant play during hard acceleration. I assume the 'brim' of the 'top hat'-looking regulator is a diaphragm.

                              Agree, moving along. Plenty of rail pressure. I need to pull the boat to my house so I can delve into the VST and HP pump filter and the fuel injectors. I am also suspecting bad fuel. Thanks.

                              As an aside, it would be nice if the VST could be modified with maybe a 1 inch diameter side access 'hatch', like a screw on gas cap, level with the HP pump filter so that the filter and VST interior could be inspected without ripping the VST off the engine.

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