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Replaced fuel pump --- now get backfire!-gctid828986

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    Replaced fuel pump --- now get backfire!-gctid828986

    Replaced the mechanical fuel pump on my 5.7L 2bbl Merc. Also the fuel filter/water separator (I had already drained the oil). After tightening all lines and adding oil, gave it a crank. Crank crank crank nothing. Repeat ad nauseum. Pulled the line back out of the carb and had the admiral watch for fuel. Nothing. For a loooooong time. Frustrated, sat and had a beer. Back to the helm and cranked some more. Really frustrated. One last crank and this time fuel spits out the line! Yea!!! Hook the line back up to the carb, clean up the spill and crank. Nothing. Long story short, it took a while but finally caught and started up. YEA AGAIN! Let it idle a while till I saw the temp hit 140. Tried to review it up and it stalls. Started right up, but when I try to put the throttle down it stumbles,stalls, this time with a backfire. Start it up, let it idle a while more, the give it gas very slowly. It hits but gets up to 2k the 2500. Back to idle it stalls. Start it up and try WOT and it backfires then stalls.

    Made sure I kept the fuel lines clean etc during rebuild. Only difference between today and last time running is that today it is in the low 60's temp wise. Maybe the choke? Can that be disabled as if it were hot outside by disconnecting the + wire going to it?
    2004 Monterey 282 Cruiser
    Twin Volvo Penta 5.0GXi-E
    SX-M 1.6gr Outdrives
    Docks @ Punta Gorda, Florida

    #2
    A good fuel pump should easily pump gas right away. I would remove the fuel tank pick up and inspect it, sounds like it's got blockage.
    1997 Maxum 2400 SCR 5.7LX Bravo II

    Mike

    Comment


      #3
      Also is this a backfire out the exhaust, or a POP through the carb? A pop through the carb is usually a lean pop due to not enough fuel.

      Follow Mike's advice above and let us know.
      Joel
      1987 3818 Hino 175
      "Knotty Girl"
      Prince Rupert B.C.

      Comment


        #4
        Agree, sounds like fuel starvation either a blockage or a faulty new pump :S
        Dave
        Edmonds, WA
        "THE FIX"
        '93 2556
        Carbureted 383 Vortec-Bravo II 2.0:1 18 1/4x19 P

        The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
        Misc. projects thread
        https://www.baylinerownersclub.org/f...56-gctid789773

        Comment


          #5
          A "pop" out the carb. I had (perhaps erroneously) chalked it up to having to suck up a lot of fuel to refill the now empty supply line/new filter assembly. It hadn't ever hesitated or popped before, so it was more frustration at the end of the day. Changed it on the advice of the local shop tech due to gas in the crankcase. Also saw on the MC parts site that there is a small filter at the carb which I didn't change, so will do that today and then see if the oil level is ok with no additional level increase.

          Always appreciate the guidance from folks here. Thanks.....
          2004 Monterey 282 Cruiser
          Twin Volvo Penta 5.0GXi-E
          SX-M 1.6gr Outdrives
          Docks @ Punta Gorda, Florida

          Comment


            #6
            A marine fuel pump has two diaphragms with the area between them connected to a sight tube that goes to the carb. From what you are saying both diaphragms must have been leaking to get gas in the oil and the sight tube should have had gas in it as well.
            1997 Maxum 2400 SCR 5.7LX Bravo II

            Mike

            Comment


              #7
              Thanks. If the site glass is the yellowish tube going back to the carb, it was hard, no longer "visible" due to having turned opaque. Also once removed at the carb fitting it seemed to be blocked. Removed the fitting from the carb and found it to be totally blocked with some green crud. Couldn't get air through it until I cleaned it out with a small dental pick. Got a new MC (OEM) hose and installed it during replacement. Thinking that if the pump was trying to push fuel up that hose it wouldn't have been able to overcome the blockage, and I wouldn't have seen fuel in the hose as it was no longer clear. By the time I removed it it had been sitting a couple weeks, so fuel may have drained back down the tube perhaps?

              Couldn't upload pic of tank pickup point, but will look at that possibility. Also going to do compression check, but if I am not getting gas in the sump anymore I suspect it would point to the old pump.
              2004 Monterey 282 Cruiser
              Twin Volvo Penta 5.0GXi-E
              SX-M 1.6gr Outdrives
              Docks @ Punta Gorda, Florida

              Comment


                #8
                Thanks. I'll check to see if I can get the pickup out of the tank. Is the "anti siphon" valve also inside as part of the pickup? My hose attaches at the yellow circle.


                Attached files

                2004 Monterey 282 Cruiser
                Twin Volvo Penta 5.0GXi-E
                SX-M 1.6gr Outdrives
                Docks @ Punta Gorda, Florida

                Comment


                  #9
                  When you remove the pickup ( it screws out ) yes the anti-syphin valve is the fitting, check it isn't blocked, if this were my boat I would suck the gunk and junk off the bottom of the tank.

                  Should preform a pressure test on the tank.
                  Be good, be happy, for tomorrow is promised to no man !

                  1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

                  '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

                  Manalapan N.J

                  Comment


                    #10
                    Thanks Chief. I pulled the small filter in the carb, and it was full of fine crud, so suspect you are correct about the pickup/tank having crud in it as well. Don't know how long the filter has been in there, and it may be that some of that has gotten into the carb where it shouldn't be. Question - if I pulled the hose to the tank off and placed it in a 1 gallon can of fresh clean gas, would that work? And perhaps solve the flow/pump vs tank question?

                    Old pump site tube:



                    Old carb filter:



                    Took some video but it doesn't seem to upload.
                    2004 Monterey 282 Cruiser
                    Twin Volvo Penta 5.0GXi-E
                    SX-M 1.6gr Outdrives
                    Docks @ Punta Gorda, Florida

                    Comment


                      #11
                      "pgiconch" post=829048 wrote:
                      Thanks. If the site glass is the yellowish tube going back to the carb, it was hard, no longer "visible" due to having turned opaque. Also once removed at the carb fitting it seemed to be blocked. Removed the fitting from the carb and found it to be totally blocked with some green crud. Couldn't get air through it until I cleaned it out with a small dental pick. Got a new MC (OEM) hose and installed it during replacement. Thinking that if the pump was trying to push fuel up that hose it wouldn't have been able to overcome the blockage, and I wouldn't have seen fuel in the hose as it was no longer clear. By the time I removed it it had been sitting a couple weeks, so fuel may have drained back down the tube perhaps?

                      Couldn't upload pic of tank pickup point, but will look at that possibility. Also going to do compression check, but if I am not getting gas in the sump anymore I suspect it would point to the old pump.
                      Yes the sight tube is yellowish and connects to the carb. If the fuel pump diaphragm leaks fuel shows up in the tube and is routed to the carb to prevent it from spilling into the bilge.
                      1997 Maxum 2400 SCR 5.7LX Bravo II

                      Mike

                      Comment


                        #12
                        "Chief Alen" post=829052 wrote:
                        When you remove the pickup ( it screws out ) yes the anti-syphin valve is the fitting, check it isn't blocked, if this were my boat I would suck the gunk and junk off the bottom of the tank.

                        Should preform a pressure test on the tank.
                        Yes the anti-siphon valve is built into the barbed section that the hose is attached too.
                        1997 Maxum 2400 SCR 5.7LX Bravo II

                        Mike

                        Comment


                          #13
                          "pgiconch" post=829061 wrote:
                          Thanks Chief. I pulled the small filter in the carb, and it was full of fine crud, so suspect you are correct about the pickup/tank having crud in it as well. Don't know how long the filter has been in there, and it may be that some of that has gotten into the carb where it shouldn't be. Question - if I pulled the hose to the tank off and placed it in a 1 gallon can of fresh clean gas, would that work? And perhaps solve the flow/pump vs tank question?

                          Old pump site tube:

                          [attachment]42417 wrote:
                          OldPump.jpg[/attachment]

                          Old carb filter:

                          [attachment]42418 wrote:
                          OldFilter.jpg[/attachment]

                          Took some video but it doesn't seem to upload.
                          Yes you can run the engine from an external tank but use caution that fumes are not present. I prefer using an outboard tank that you can connect the hose to a barbed fitting, just use straight gas though.
                          1997 Maxum 2400 SCR 5.7LX Bravo II

                          Mike

                          Comment


                            #14
                            Agree with Mike, run it off an outboard type fuel tank. Replace all fuel lines if you haven't already done so, old lines will come apart on the inside causing more crud in the fuel system.
                            Dave
                            Edmonds, WA
                            "THE FIX"
                            '93 2556
                            Carbureted 383 Vortec-Bravo II 2.0:1 18 1/4x19 P

                            The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
                            Misc. projects thread
                            https://www.baylinerownersclub.org/f...56-gctid789773

                            Comment


                              #15
                              UPDATE: just sat down with a beer. This time to celebrate. The admiral interupted my morning work to take her to pick up some stuff at the store. On the way home I stop and get a can of Seafoam carb cleaner. I check the oil level - it was right where I put it yesterday (half way between the add n full marks). Crank it up, it stumbles at throttle up, pops and coughs just as before. Dies. Start it again, get it up to about 1500rpms and start applying the seafoam. It bogs with each squirt but recovers. Keep it up and notice it doesn't stumble as bad when I spray in the starboard side as the port bore. Keep on spraying. Use up half a can. Let it idle, then ran it up to 1000rpm and let it run for a half hour. Go back and check on it and it seems to rev ok without the stumble. Let it run another half hour, rev it up.....no stumbling. Turn it off. Started right up, idled nicely, and revved really well....better than before. No backfires!!! Let it sit 5 minutes and checked oil. Down to the add mark which is ok. Took the admiral on another buying expidition. Get back after a couple hours and check oil.....right exactly between the add and full mark. PERFECT!! Cranked it up, and it is purring as it did before. Happy camper again.

                              With that said I know I need to do a tank cleaning (for no other reason than it is old and there HAS to be crud in there). But I need to get it hauled out to have the stern drive water pump seal repaired (slight oil leak out the water intake) and a new prop put on. I also want to put an oil filter adaptor on it (don't know if I can do that or not) because changing the filter in the low block position was messy and an extreme pain in you know where. Along with a hundred other places. I also have plugs, wires, Dist cap/rotor and coil parts to put in. One thing at a time though.

                              If the oil has no gas in it by tomorrow and level is still midpoint I'll call this issue a wrap and move on to all the other items. As time permits around the admirals schedule of course. I have found that being retired only means the Admiralty gets more of your day than before!!

                              I really appreciated all the feedback and help. You were all correct that it was a fuel flow problem.
                              2004 Monterey 282 Cruiser
                              Twin Volvo Penta 5.0GXi-E
                              SX-M 1.6gr Outdrives
                              Docks @ Punta Gorda, Florida

                              Comment

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