wavy fuel pump

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  • diesel71
    Senior Member
    • Feb 2008
    • 921

    wavy fuel pump

    I thought I would post this to help anyone that has current ramped a transfer pump on a 2015 6.7 diesel. this vehicle came in with just a loud/noisy pump, runs fine no check engine lights. ok confirm filters were changed and fuel in the tank. hooked-up pressure transducer, fuel pressure at 69psi in specs. connected low amp clamp on pump + feed wire,set scope at 10 amps no signal. set scope to 5 amps no signal then again to 2 amps and bingo have a signal that seems to be drawing very little amps to work.
    watch the wave forum for a few seconds and it looks like a roller costar?
    bad pump? im not sure at this point so I see a repeating pattern and count 12 commutator bars not the usual 8. use the scope cursors to get the pump speed, 60,000 divided by 18.65 =3,217rpm not the usual 6,000 rpm. I cant condemn the pump at this point. customer wants it replaced anyway so I get the chance to dissect the pump and check what the scope was showing me. dissect the pump and sure enough 12 commutators, the roller costar waves on the scope are from the pump shoes. there are 5 round pump shoes and when one passes by the squeeze point it causes 3 or 4 commutator bars to draw more amps. the noise was from a bad upper armature shaft bearing. pulled a different 2015 truck in and current ramped the pump, got the exact same pattern and pressure. this just taught me the scope never lies and a steady wave forum is not what you are always going to see.
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  • greasybob
    Senior Member
    • May 2008
    • 1590

    #2
    Interesting, I see it says 6.7 Ford on the scope file viewer. It is a Ford and not a 6.7 RAM correct ?

    Comment

    • diesel71
      Senior Member
      • Feb 2008
      • 921

      #3
      Originally posted by greasybob
      Interesting, I see it says 6.7 Ford on the scope file viewer. It is a Ford and not a 6.7 RAM correct ?
      correct bob this was a 2015 ford f-550. the 6.7 dodge/Cummins have a transfer pump too but they are in the tank. who knows if they are the normal 8 commutator or not, ill check the next one I see.

      Comment

      • sbreland73
        Senior Member
        • Jan 2009
        • 1076

        #4
        Nice leg work! Thanks for sharing your findings with the rest of us.
        S. Breland

        Comment

        • greasybob
          Senior Member
          • May 2008
          • 1590

          #5
          I curious how you tested the lift pump output pressure. I have one here and don't see a schrader valve and only a low pressure switch not a sensor for the PCM.

          Comment

          • diesel71
            Senior Member
            • Feb 2008
            • 921

            #6
            Originally posted by greasybob
            I curious how you tested the lift pump output pressure. I have one here and don't see a schrader valve and only a low pressure switch not a sensor for the PCM.
            your right bob there is only the low pressure switch. what I did is use the snapon fuel pressure test set #eedf502. it has a quick connect tee hose assembly, that has the right quick connect fitting to tee into the filter line on the frame mounted filter or the engine mounted filter. I just adapted the coupler to my pressure transducer. could you current ramp that pump and shoot me a screen shot or movie?. id love to see what you get?

            Comment

            • greasybob
              Senior Member
              • May 2008
              • 1590

              #7
              I'll post it here in hour or so.

              Comment

              • greasybob
                Senior Member
                • May 2008
                • 1590

                #8
                Ok, for what it's worth. I tried to duplicate your test as close as I could. My fuel pressure seems a little lower. To get the fuel pressure I removed the low pressure switch and put my transducer with an adapter into the port. Maybe the pressure is lower here on the other side of the secondary filter. this is also a key on engine off test. This pump is quiet, the truck is a 2013 with 22,000 miles.
                Attached Files

                Comment

                • greasybob
                  Senior Member
                  • May 2008
                  • 1590

                  #9
                  I see my pump is also about 20% slower. I finally got this thing running. It's a long story. Still has a few issues. I'll try and check the fuel pump again tomorrow with the engine running.

                  Comment

                  • diesel71
                    Senior Member
                    • Feb 2008
                    • 921

                    #10
                    Bob, thank you for taking the time to do this, its great to compare. now we know what the pump wave forums should look like on these pumps.
                    yours was a little slower with less pressure, my transducer was on the inlet side of the small engine mounted filter, your pressure may read lower because its after that filter. one thing that don't make sense to me, the pump circuit uses a 20amp fuse yet the amp draw is extremely low??
                    correct me if im wrong, more commutator bars would take less amps to move the armature and pump?

                    Comment

                    • MonzaRacer
                      Member
                      • May 2008
                      • 44

                      #11
                      Fuses are too protect the circuit. The rating is what the wiring and connectors need protected to. So the circuit won't burn up.
                      Also probably rated for maxed out pump load through stopped up filter.

                      Comment

                      • Crusty
                        Senior Member
                        • Dec 2007
                        • 2450

                        #12
                        Originally posted by MonzaRacer
                        Fuses are too protect the circuit. The rating is what the wiring and connectors need protected to. So the circuit won't burn up.
                        Also probably rated for maxed out pump load through stopped up filter.
                        It's normal for any winding to have an inrush surge current. If the pump is designed (by wire size and length...not number of commutators) to run at 7 amps the minimum surge would be expected to be easily double a normal running current, ie; 14amps. To protect the overload possible along with the inrush, they selected 20 amps instead of 15.

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