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Yamaha F115 EFI -02 running rough and low power

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  • Yamaha F115 EFI -02 running rough and low power

    Hi, first I want to thank the forum users as I have got more knowledge than before from reading here for a couple of years.

    Now feel the need to post a question about my F115 with 500 hours on it and it has been running rough on idle for the 2 years I had it but always ran OK when in gear. But now something else happened and it didnt run properly when in gear and I could not get full power. almost like it ran on 3 cylinders.

    YDS says that water temp sensor is bad. error code 15. I have a new sensor on the way. My question is if the sensor has anything to do with the isc valve opening?
    I get a strange number on ISC valve opening from YDS. I get 50%opening at idle 750 rpm and 53 % at 1600 rpm and 59% at 2870 rpm. Seem very low compared to what others have reporting here in the forum. For example Rodbolt said that ISC should go to 100% when >1300 rpm. I can here the ISC rattle when turning the engine of.

    My tps voltage is 0.728 at idle. My other YDS numbers such as intake pressure etc is in the same range as others in the forum and seem normal.

    I have cleaned the injectors and VST. exchanged the LP pump and I also here the High pres pump spin when key on.
    Changed the ign coils and plugs. I got a lot of parts from a used F115.

    Also when I unplug the Isc there is no real differens in idle. Did the active test with YDS and increased RPM when Increased ISC valve opening. Can I rule the ISC out ?

    When I pull the vacuum hose from regulator and pinch it I do NOT get an increase in RPM nor is there any gas leaking out of it. If i just pull the hose the engnge dies.

    My nr 1 plug is sooted and wet from I think gasoline. it smells so. Probably nr 1 is misfiring?

    Also been running on seperate fuel tank and exhanged the inline filter. I pump the bulb but it does nothing for the rough running.

    Next I think I will swap the ECU for my spare one and also try to do compression test and leak down but I need to buy the gauge first.

    Anyone have any suggestions? This is driving me mad. I was thinking T-stat but it should not matter when engine is cold? it misfires from start and the idle is not fixed. it is varying about 30 rpms up and down.

    What symptoms can water temp sensor cause? Someone wrote about it messing up all kind of things on his F115 but I cant really understand what it does, or how the ECU uses it. besides alarming if to hot.


  • #2
    I am not sure on your motor, but some times a bad water pressure or was it a temp sensor could leak water up into the wiring affecting voltages to more sensors.
    have you checked the 5 volt sent to sensors to make sure it was OK


    • #3
      Thanks. Will test the reference voltage. There has been water present under the cowling after raining. I tried to seal that air intake gasket a couple of days ago. Maybe that whater have shorted the sensor or something.
      Still finding it strange that the ISC request is too low when reving up. Also strange that it doesnt matter if I disconnect it as I can hear it rattle at shut down and also were able to control it with the YDS. Also it feels strange that I have a low idle and also at the same time a error code on temp sensor. Should result in 1100 rpm idle ? I had high idle before but adjusted the tps that was way of according to YDS. Then it ran properly but still idled rough and traces of waste gas in the sea. Looks real bad when stopping in a harbour and there is gas/oil in the water behind the motor.


      • #4
        Measured the reference voltage on TPS, water temp sensor, map sensor and air intake sensor. They were about 4.6 Volts and that is a little low? The IAC was 12 V approx. No difference when disconnecting sensors. still same reference.
        Also pulled the plugs and all 4 were badly fouled. almost black with sooth. a little wet also. No gas in the oil that I could identify. pumped out some oil and it was black but at least no water in it. I tried to messure Fuel pressure but the nipple did not seal properly but it squirted out when key on so at least it seem to work to some degree. HAve not gotten the new water temp sensor yet but tried both plugged and unplugged.
        Also If someone knows why the engine dies when I disconnect the MAP sensor?

        A bit lost now...


        • #5
          Those 5V numbers for the sensors look right to me. Note that the ISC isn't a sensor, so it doesn't get 5V reference.

          You replaced the plugs recently, but now they're all fouled. You also said the engine dies if you pull the vacuum sensing hose. When you pull that hose, the fuel pressure increases. If the pressure is correct to begin with, disconnecting the sensing hose should only cause it to run a bit rich (but not die). So I would say it's running too rich to begin with. To confirm that, you need to measure the fuel pressure at the VST fitting or you need to get an adapter that sits between the fuel rail and the VST. When measuring fuel pressure, there should be no nipple that needs to seal.. it should be done with a screw-on gauge.

          Assuming the fuel pressure is too high, that could be a suck pressure regulator (that is keeping the fuel pressure too high), or stuck/clogged injectors. If you find that the fuel pressure is within spec, then I would have to assume it's a stuck ISC that's not letting enough air in. Yamaha doesn't tell you how to clean the ISC, but it seems you should be able to spray electrical parts cleaner through it. I would also double-check your linkage just to rule that out.
          2011 F50TLR, 2010 G3 V167C


          • #6
            Thank you Rejesterd
            The engine dies when taking the vacuum hose of without pinching it. I guess the pressure in the intake goes up, or vacuum down. I dont know if that is normal. However there is no increase in RPM from taking tha hose of and putting my thump over the hole in the hose.
            I Will Try to clean the ISC as I found a thread on a guy having issues with it even though the "Rattle" was there as it is for me.
            Will also try to find a correct connector for the shrader valve for fuel pressuer montoring.


            • #7
              Originally posted by metallifredd View Post
              Thank you Rejesterd
              However there is no increase in RPM from taking tha hose of and putting my thump over the hole in the hose.
              Right, there shouldn't be an increase in RPM. The pressure regulator controls fuel pressure only. The ECM (via the sensors) and the throttle plate's position determine the RPM. That's why if you disconnect the vacuum sensing hose, it will run richer (and will die if it's already running too rich to begin with). The computer doesn't know what the fuel pressure is.. it assumes that it's at a certain value (identified in the service manual) and it assumes that the sensing line is connected and restricting the pressure slightly (which allows the pressure to rapidly increase if the throttle is opened quickly).
              2011 F50TLR, 2010 G3 V167C


              • #8
                Hi again. Now I am really baffled. The arrows on my timing belt wheels do NOT align. They do not point at each other. I post a pic that is showing the timing belt.
                If it is wrong then I cant really understand that the motor have been working almost good?


                • #9
                  Sorry but I just realised that the alignment is only at one point and the pic shows that the both wheels are about the same distance from pointing towards each other. Stupid me...


                  • #10
                    The engine should be at TDC on the compression stroke for everything to align..

                    The flywheel should align as well with a mark (usually a timing mark indicator).
                    1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR


                    • #11
                      Did you resolve this issue? I have a misbehaving 2006 F115. Thanks