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Suzuki DF90 runns rough on mid range to high RPM

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  • Suzuki DF90 runns rough on mid range to high RPM

    Hi. My 2001 Suzuki DF90 starts and runns normal. When I put it in gear it keep running smooth until I hit about 3000 RPM - then it starts running rough. If I keep the throttle steady the engine sometimes runns fine for a few seconds before it goes back to running rough. When I reduse the RPM to below 3000 it will keep running rough - but runns smooth if I stop and start it again. I had some water in the fuel system last fall so I thought that was the issue. I have cleaned the tank, replaced the water separating fuel filter, low pressure fuel filter and high pressure fuel filter and cleaned the VST tank. This had no effect on the issue. My next guess would be the injectors or som kind of sensor issue. There are som fuel getting through to the oil system too. Any suggestions?

  • #2
    Have a read of this thread, it may be relevant.

    https://www.suzukioutboardforum.com/...-motor-studder

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    • #3
      Originally posted by Moonlighter View Post
      Have a read of this thread, it may be relevant.

      https://www.suzukioutboardforum.com/...-motor-studder
      Thanks for the reply Moonlighter. I'll definatly check out the Neutral switch, and try to bypass it. Yesterday I tested the low pressure fuel pump, as a leakage in the pump would "make oil" in the engine - but the pump seems fine. I'm away for a few days, so I'll try again on sunday or monday. My next move is to bypass the Neutral switch and try to clean the injectors.

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      • #4
        A little update - and more questions

        I put the fuel pump back, and got the motor diagnosed. The software showed that the IAT sensor had failed one time. Other than that there where no faultcodes active. When testing the fuel injectors I had positive results in three of the "Injector - stop - test"(engine stalling). In the fourth injector there where no change in how the motor ran. Thinking this could be due to a faulty injector i removed the fuel rail and cleaned all four injectors. When I put it back, I changed the order of #1 and #4 to see if any problems would change from cylinder #4 to # 1. Unfortunatly there where no changes to the engine - and it was still cylinder #4 causing the issue. The next thing I did was to run a compression test to all cylinders. The test ranged from 14 - 17 (And normal compression is 13 - 17). When I put the ignition plug wires back, I wiggled it a little, and a light "click" sound implied that something happend. Although I had run ha spark - test earlier, I might have been lucky running this test, as there seems to be a bad connection. Now the motor runs more smoothly and reaches 5500 rpm (normal is 5700 at max) but It makes a terrible "crackling" noise at some RPMs, and it also appears to lack som of the accelration I used to have on the boat. I will order 4 new ignition plug-wires just to see if it helps the engine running more smoothly, and also change oil and filter again since it is a bit of fuel in the oil. (I hope this is caused by running the engine on three cylinders while testing it - and that this will solve the issue).

        Does anyone have any idea of what can make this "crackling" noise? It sounds like a leak in the exhaust-system, but maybe there is some other explaination. Could a faulty IAT sensor cause these problems? The engine runns normal at low RPM, and at some ranges as I throttle up.

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        • #5
          Rufsen,
          Any updates for us?

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          • #6
            Originally posted by Skiffmate View Post
            Rufsen,
            Any updates for us?
            Hi. I've been busy at work the last week, så I haven't had the time to do much until today. Three of the plug wires are in stock in Norway - but the one I need isnt. So I have to wait. In the meantime I have changed the gas-mixed-oil, and replaced it with new oil. There are still some trace of gas in the oil - but this is most likely "leftovers" as I did not change the fuel-filter. The engine is now running smooth, but still with the enoying "crackeling" sound when I reach a surtain RPM. The engine is no longer "making oil", så I guess the reason for this was that was the engine running on three cylinders. (I checked the vapor-hose from the VST tank - and it only expelled fumes (no liquids)). I've talked to a mechanic who will come with me to see if he can identify the noise (hopefully today). I'll take the boat out of the water soon, to change the oil again, and also the filters. I'm afraid that the sound is a bad bearing or mechanical wear and tear.

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