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  1. #1

    Spark Plugs vs Fuel Pump

    One of my skis I was certain had fouled plugs. So I changed them and it ran great for awhile (first 20 minutes or so). Then after a 10 minute slow zone, started banging out real bad. So I'm thinking these plugs are fouled again from all this idling. So we switched riders (I am now on problem ski) and I slowly added power until I'm doing 58 or so, engine purring along smooth as glass at 7200 rpms and 12" ish boost.

    Of course the bud that was riding it looking at me like I'm crazy after I announce, "Working fine now." After awhile it started doing it again real bad/occasionally dying completely. It would restart and run fine for a few seconds then quit again or run like it was on one cylinder.

    Bottom line is I think fuel pump is dying. How have you guys diagnosed this in the past? I'm not interested in seeing how much fuel it will spit into a cup over 3 seconds or whatever due to the intermittent nature of the problem. I'm thinking put a "T" in the fuel line going to a gauge I can see while riding it. Anybody else tried something like this?


  2. #2
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Pretty standard to check the fuel pressure with a gauge inline like you are talking about doing. The intermittent nature of it makes me think it could be bad gas or water as another potential.

    Sean


  3. #3
    Both skis been run frequently this year and I only put ethanol free 93 octane in them. I also use StaBil in the fuel caddy/gas cans.

    How have guys run the hose from the engine compartment up to where you can see the gauge without the seat crimping the line?

    Thanks SS

  4. #4
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Quote Originally Posted by Cranofwaterfell View Post
    Both skis been run frequently this year and I only put ethanol free 93 octane in them. I also use StaBil in the fuel caddy/gas cans.

    How have guys run the hose from the engine compartment up to where you can see the gauge without the seat crimping the line?

    Thanks SS
    I would start by checking static pressure on key on/just after you bump the starter motor. If that jumps up to spec, you can then start the engine and watch it again. If that checks out, run it up though one of the vent tubes or out the hood.

    Sean

  5. #5
    Take the time to smile sirbreaksalot's Avatar
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    Quote Originally Posted by Cranofwaterfell View Post
    One of my skis I was certain had fouled plugs. So I changed them and it ran great for awhile (first 20 minutes or so). Then after a 10 minute slow zone, started banging out real bad. So I'm thinking these plugs are fouled again from all this idling. So we switched riders (I am now on problem ski) and I slowly added power until I'm doing 58 or so, engine purring along smooth as glass at 7200 rpms and 12" ish boost.

    Of course the bud that was riding it looking at me like I'm crazy after I announce, "Working fine now." After awhile it started doing it again real bad/occasionally dying completely. It would restart and run fine for a few seconds then quit again or run like it was on one cylinder.

    Bottom line is I think fuel pump is dying. How have you guys diagnosed this in the past? I'm not interested in seeing how much fuel it will spit into a cup over 3 seconds or whatever due to the intermittent nature of the problem. I'm thinking put a "T" in the fuel line going to a gauge I can see while riding it. Anybody else tried something like this?
    If your not interested in diagnosing it correctly via trusted methods ........... then I say good luck

    Pressure is irrelevant without flow............

    bad gas would produce a constant problem...

  6. #6
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Good point Waz, I was thinking minimal water in the tank but enough to float near the fuel pickup but move around as the ski moves. Bad gas is just bad so you are right, it wouldn't vary within a tank.

    I need to stop posting while tired lol

    Sean

  7. #7
    Quote Originally Posted by sirbreaksalot View Post
    If your not interested in diagnosing it correctly via trusted methods ........... then I say good luck

    Pressure is irrelevant without flow............

    bad gas would produce a constant problem...

    Exactly my point; it is NOT a constant problem and as I stated above, gas is fresh 93 octane. I'm quite sure if I did the quantity check for 3 seconds it would be the correct amount. What I'm trying to determine is what the fuel pressure is when it starts running bad/dying on me.

  8. #8
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    Last year I had a customers 15F behaving this way. He assured me only good gas, well maintained. After I test rode it I thought, hmmmm, maybe fuel pump. Took fuel line off and bumped it over.....filled a cup mostly with milky fuel. Fuel filter was also almost full of water. Also siphoned out about 3 gallons off the bottom of his tank.

    It happens.....you can get bad gas even if you think it's good.

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  10. #9
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    The 15f fuel pumps can have issues with the wiring that goes from the bulkhead connector in the top of the pump to the internal wiring harness. The connector can be loose and allow the wires to vibrate or wiggle which causes the pump not to work as it should. Might be something to look at.

    Sean

  11. #10
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    After 445hrs on my ski/fuel pump this is what I needed to diagnose the bad pump. 40$ is in parts. Mine passed the fuel flow test into the cup but wouldn’t run good past 5500-6000

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