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1998 Volvo Penta 5.0 Gi (50FBPBYC) Idles fine but boggs down when throttling

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  • 1998 Volvo Penta 5.0 Gi (50FBPBYC) Idles fine but boggs down when throttling

    Hi there, After a long time I finally joined the used boat owner community! Got myself a 1998 Four Winns 225 Sundowner with 200 hours on the engine. The boat is in great shape and has always been maintained by the boatyard mechanic. The engine idles fine but when I hit the throttle, the engine revs up for a few seconds and starts to bog down and dies. When purchasing the boat I was aware of the issue, talked to the mechanic who took care of the boat and he mentioned it needed a fuel pump. He did not specify HP or LP pump. A quick pressure reading revealed a HP discharge at 29 psi and a LP (measured at the valve located on the lid of the VST) to be at 0 psi. I went ahead and replaced the LP fuel pump last night and the problem still occurring. I have not taken a pressure reading at the VST yet after pump install.. I ran out of day light! When I turn the key to the on position (engine off) both pumps cycle (can feel and hear pump cycling for a couple seconds), the engine fires right up and idles great however it is bogging down when I hit the throttle. At this point I am ruling out a bad fuel pump. I have yet to feel or hear teh LP pump cycling while the engine is running. Could there be an issue with the fuel pump relay? I do see two relays on the relay bracket next to the LP fuel pump.. Diagrams only show one relay required. Not sure if one of them is a spare..

    I have checked the carb throat and did observe gas flow into the carb, I have checked all lines for blockage (found none), I have opened up the VST and found it to be clean (with gas of course), gas filter was replaced by boat yard mechanic this season and was also found to be clean. Pulled the float and dip tube (with check valve which was clear) from gas tank and had no indication of dirt, gunk or debris. gas in it seemed fine and clean.

    Before replacing the LP fuel pump, I did mess with the connections of the fuel pumps and for a second I was able to get the engine to rev up without dying and after a little while I got a little bit of smoking (grayish), checked the water coming out of engine and did find it a little hot.. Not sure if the engine has a history of overheating but I did take the thermostat hosing and cleaned it up including replacing the thermostat. I have not seen a high temp alarm yet.

    Does anyone have any idea of what could be causing this problem? Any help is appreciated!!

    Ps: I am not an expert mechanic but do like to tackle most problems myself (when possible), I hope I can get this fixed given some help!

    Thanks in advance!
    Carlos

  • #2
    How does the underside of the cap look? Maybe time to replace the cap and rotor as well as plugs?

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    • #3
      The distributor cap looks to be the newest part on the entire engine. Although this boat was maintained by a boatyard mechanic, I was quite disappointed with all the dirt and grease all over the engine and engine compartment. The cap and cables are the only think that looks clean so I am assuming they were replaced somewhat recently. I will take a look at the underside of the cap and report my findings. I am trying to clean things as I take them apart but definitely need to spend some time doing an engine and compartment clean-up.

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      • #4
        Have you checked the fuel tank pick up pipe and for dirt in tank.
        This being the case, the engine will often run fine at low revs and all will appear to be clear when not running.
        As the engine revs and demands and sucks more fuel, it draws the dirt and crap in fuel tank hard enough to block the pick up gauze in tank.
        Worth a quick look.
        If able, pull he pop and inch up of the bottom and try it then or run from an outboard tank with good fuel.

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        • #5
          Pulled the tank pick up pipe and float, no blockage.. also looked into the tank and had no debris.. will try over the weekend to run off a portable tank with freah gas just to rule out bad gas..

          Also took the manifolds apart today and checked the exhaust flappers.. was afraid they may have been **** closed causing back pressure.. they were both stuck open and not moving very freely.. went ahead and pulled them off since they werent doing me any good stuck open. Also disconnected the fuel relays and put them back on.. not sure if it will do anything but it is worth a try i guess.. Will finish reassembling the second manifold tomorrow and will try to run the engine again to see if anything has changed before taking the cap off to check for corrosion and checking plugs and cables..

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          • #6
            Does the pump stay at 29 psi when throttling up? Or was that just a static check?
            sigpic2001 Stingray 200LX "2 TIMING"
            1974 Rogers Bonneville Jet

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            • #7
              Originally posted by gbeltran View Post
              Does the pump stay at 29 psi when throttling up? Or was that just a static check?
              The pressure reading was taken during idling.

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              • #8
                Update:

                Finally got around to re-assembling the last exhaust manifold. I also disconnected power to try and clear any codes that may have been present. Fired up the engine and although the engine boggled down once, I was able to rev up the engine a few times without it dying on me. I did observe a little dark smoke when warmed up. I could not judge the color as by the time I got it running it was a bit dark already.

                Anyways.. Went ahead and took the distributor cap and rotor off and found some corrosion on the pins of the cap (the ignition module looks good). Have parts on order for replacement and should be able to put it back together in a couple days to see how it runs. Also got some carb cleaner spray to try and get the carb cleaned up a bit, there is quite a bit of grease and gunk on the throttle lever which is not moving very freely.. I will let you know how it turns out.

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                • #9
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                  Update:

                  Got the rotor and cap back together last night and fired up the engine. The engine is running strong and I was able to slowly rev up the engine without it boggling down and dying on me. Also, the engine de-accelerated just fine and went back to a nice idling when I let go of the throttle (engine would stall before). Im going to clean things up a bit and then hopefully do a water test this weekend (weather permitting). Thanks for everyone's help this far!

                  Stay tuned for updates!

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