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More musings on temperature sensors (Fairdeal?)

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  • More musings on temperature sensors (Fairdeal?)

    The two wire sensors we recently talked about have both wire leads (both B/Y) connected to the CDI/ECU. Leads me to believe they are like the system I found where the ECU outputs X voltage and is measuring the input voltage through the sensor so as to derive the air temperature or engine temperature.

    I now see that Yamaha uses a black lead and a black/yellow lead in the wire harness for the sensors on later models. Black being ground. Presumption being that B/Y is the output voltage as you measured on your motor. The black lead connects to a common ground junction box.

    Since the ECU appears to now not be measuring input voltage back to the ECU I am presuming that the ECU might now be measuring current flow out from the output lead so as to derive a temperature value.

    Have you any idea as to what may be going on?

  • #2
    Originally posted by boscoe99 View Post
    Since the ECU appears to now not be measuring input voltage back to the ECU I am presuming that the ECU might now be measuring current flow out from the output lead so as to derive a temperature value.
    [/IMG]
    Interesting to see the "older" diagram with both leads "coming off" the ECU - was not aware of that.

    My assumption for the devices used on my F225:
    one lead from the ECU, then through the sensor to ground -

    is that they are working exactly like a fuel gauge (or trim gauge) does:

    where the gauge "measures the current flowing through the sensor to ground"

    (alternatively expressed as "measures the resistance of the sensor")

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    • #3
      my guess would be for biasing the base of a transistor.
      that is what they do.
      bias it enough and it switchs ON.
      that and the arrows and boxes lead to the wrong connectors .

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      • #4
        Originally posted by rodbolt17 View Post
        my guess would be for biasing the base of a transistor.
        that is what they do.
        bias it enough and it switchs ON.
        that and the arrows and boxes lead to the wrong connectors .
        They do don't they?

        Yamaha makes it challenging to trace wires from one point to another. Maybe they got me on this one.
        Last edited by boscoe99; 09-12-2018, 08:50 PM.

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        • #5
          Originally posted by fairdeal View Post

          Interesting to see the "older" diagram with both leads "coming off" the ECU - was not aware of that.

          My assumption for the devices used on my F225:
          one lead from the ECU, then through the sensor to ground -

          is that they are working exactly like a fuel gauge (or trim gauge) does:

          where the gauge "measures the current flowing through the sensor to ground"

          (alternatively expressed as "measures the resistance of the sensor")
          Your comment on the fuel gauge or trim gauge is what caused me to think this might be what is happening in the later model Yams.

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          • #6
            Yamaha is getting better than the old 1990's manuals. but not near as good as mercruiser or Volvo.
            only reason I spotted it is cause I have been dealing with diagrams for a living since I joined the navy in 88

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