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2005 5.7 gx-f stumbles @ 900-1100 RPMS

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  • 2005 5.7 gx-f stumbles @ 900-1100 RPMS

    hey GUys i need some help, i have a 2005 gx that was running poorly and intermitently no start. the fuel pump terminals were all corroded and the pump was not working properly so that was replaced, then it would run fine but not great.and developed a stumble @ 900 through 1100RPMS. then it would smooth out. the whole boat would shake. the cap was corroded so the cap/rotor and plugs were replaced. with no change. then it stopped running entirely. diagnostics found that the coil output was very weak so the coil and wires were replaced. the boat now runs but the same stumble is still there.
    i have verified the low and high fuel pressure, the spark is fine. the injectors are firing properly and i did a fuel injection cleaning on them. i did a cylinder balace test using the rinda scanner and all cylinders seem to react the same.
    im stumped on this one.
    any help is always appreciated

  • #2
    verified the low and high fuel pressure, the spark is fine
    Does the fuel pressure stay steray as it goes thru the rpm band?

    Connect the scanner and watch the TPS to see if you get a smooth increase as the throttle moves. Then watch the MAP and IAC and compair with TPS operation

    TPS % goes up, MAP pressure goes down, IAC % or count corresponds to transition between 900 and 1100 rpm
    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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    • #3
      i was reviewing the tp sensor voltage and although it is smooth, and does not drop out during acceleratipon, i think it stays at .72v a bit longer than i feel it should as in, i am moving the throttle ever so slightly and the rpms increase slightly but the tps volts hold @ .72, then continues, .74,.76 etc...

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      • #4
        It should continue to move, and can be marked as an issue to watch and compare with the other readings
        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


        • #5
          OK, I finally have a moment to write this post, ive attached a spreadhseet of readings. i missed the IAC reading for 760-920 range, that reading is 27
          the boat shakes from 760rpms to 10400 then smooth at 1100 and there after
          BRIAN SCANNER READINGS.pdf

          this thing is really driving me to pull my hair out. and i dont have much left to start with.
          another thread i was reading spoke about the fuel pumps when they go bad and th epaint from inside breaks down and flakes get into the system. there has been comments about shaking and poor MPG. we dont have the poor MPG but im starting to wonder if the fuel injectors shoudl be looked at more in depth. the only thing that throughs me off is that it is not consistant and only during that small window.
          ive also read about outdrive issues but the drive was off this season and everything looks fine, the alignment is on the money as well.

          also, i unplugged the tps and the shake is still there so i kind of ruled that out as the culprit
          Attached Files
          Last edited by chs marine service; September 4th, 2019, 02:59 PM.

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          • #6
            Assuming your MAP listing is vacuum and not kPa readings

            With the motor running 1000 rpm or less, pull each spark plug wire one by one and see what the changes are. If they are all the same change then have more to look into

            Voltage from idle to 3500 + rpms, the TPS should increase close to 5V
            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


            • #7
              Are you drawing air somewhere in the fuel system ? Try bleeding the top of the fuel rails at the test point. See if you get airiated fuel

              Comment


              • #8
                Originally posted by AllDodge View Post
                Assuming your MAP listing is vacuum and not kPa readings

                With the motor running 1000 rpm or less, pull each spark plug wire one by one and see what the changes are. If they are all the same change then have more to look into

                Voltage from idle to 3500 + rpms, the TPS should increase close to 5V


                i used the rinda and did a cylinder balance test, all cylinders reacted the same

                and yes, when the throttle is open all the way, the voltage goe up to about 4.8v

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                • #9
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                  Balance test with a batch fire MPI does little to indicate much.

                  Voltage going up but nothing to indicate, goes up to what and how smooth. Is it smooth analog or some kind ot something else?
                  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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