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Does anyone know if the Sensors on a 912iS are fused in the fuse box?


While attempting to track down the cause for Lane A & B sensor faults I was informed by a Rotax "Expert" that "ALL of the sensor wiring goes through the fuse box". This was before I got my hands on a Rotax pinout/Wiring diagram of the wiring harness. I could not find any of the sensor wires that had an electrical connection to the connectors at the fuse box!

After looking at the diagram it appears that the Oil Pressure Sensor and the Ambient Air Pressure/Temperature Sensor are a direct connection from their respective connectors to the pins called out on the ECU connectors, which I verified continuity with an ohm meter.

Am I wrong and the sensor wiring does actually go through the fuse box, even though the diagram makes no mention of there being fuses for any of the sensors or pin connections for any sensors?

Everything the Expert was telling me to check makes no sense and seems to be a complete waste of time after looking at the diagram...

  • Re: What goes through the Fuse box?

    by » one month ago


    You have it right Ray, I'm afraid your Rotax "Expert" is wrong on this one.  None of the engine sensors go through the Rotax fuse box. The sensors are inherently power limited and don't need to be fused. In fact, you want the fewest point of resistance possible from the ECU to the sensor, and routing through the fuse box would only add resistance and reduce the accuracy and reliability of the sensors. 

    If your Rotax Tech needs more proof...

    There are five (5) connectors entering the fuse box: X1, X2, X3, plus the power wire connections from Alternators A and B. I have attached my pinout list, and there are no sensor connections. This is not a Rotax document, rather it's something I developed for my own use. 

    39103_2_912iS Fuse Box Pinouts.pdf (You do not have access to download this file.)

  • Re: What goes through the Fuse box?

    by » one month ago


    Jeff

    Actually all the power for the sensors is proved by the fuse box.  You are correct in that they are not fused.  

    If you care to send me your email can explain but am prohibited to distribute some for the data a have currently. 

    Cheers


  • Re: What goes through the Fuse box?

    by » one month ago


    Rotax Wizard,

    If you send Jeff an email, perhaps you can CC me on it, or Jeff can forward it to me. Thank you for your input.

    If I'm interpreting the Rotax wiring diagram correctly:

    Power to the ECU, lane A and B switches, comes from the fuse box, Correct?

    The wiring diagram does not reveal what is going on inside the black box (ECU) but, I imagine that internally, the ECU has separate power supplies for each lane, providing power at the needed voltages for the various functions. These power supplies provide the power to operate the ECU lanes and functions as well as provide the power (+5 volts) for the sensors. Each sensor has an individual wire for ground, +5v, and a Signal wire that are all home runs directly back to the ECU, Multi function sensors like the AAPT have two signal lines one for the Pressure and another for the Temp, but share the +5v and ground, Correct?

     


  • Re: What goes through the Fuse box?

    by » one month ago


    hi Ray

    I can tell you the system is fully powered via the fuse box, not the ECU.  The ECU has 2 fully separate systems.  (land A and lane B are split) Most sensors are feeding their output to the A ECU, the B is almost all fully a map system with only a few sensors for redundancy.  (the ECU has 3 connectors, 2 for A and one for B) What the ECU is reading is the resistance values for each sensor and it also knows the ambient temperatures.  In the case of fuel flow it knows the amount of fuel by the time each injector is open.  (it is a calculated flow on the ECU and not measured) Another example is lane A is the smart one, with all the sensor input.  Lane A is feed by power from the small side of the stator as it only has engine functions that include one spark set and one injector set.  Lane B is feed by the large side of the stator for power, it has one set of plugs and one set of injectors but primarily is run on an engine map and not dependent on sensor input for the most part.  The default start position, determined by the fuse box, is power comes via the large side of the stator, the map side.  Once started we need to excite the other side and to do this RPM must be over 2500.  The large side of the power generation then is used for the electrical load of the aircraft and the Lane A and B will synchronize with the sensors fine tuning the system for fuel economy.  The A and B will still have separate feed to the plugs and injectors. 

    As I have stated the full engineering drawing is not allowed for public circulation so they forbid dropping it to anyone unless an NDA is signed.  (their rules) With Clone engines already in the marketplace and other issues I think it is understandable.  

    Currently there are  few training centres who have classes on the iS systems.  I am aware of a new program that should be available soon that will be more of a diagnostic training class for technicians and with that they can release a "log viewer" to help interpret the data. This should happen the end of this year or early next. There are some instruments that will give abbreviated codes via the display, they however don't have all the data from the ECU.  it is 2 seperate ports on the system, display and ECU. The ECU has to have the BUDS connected to read. 

    Cheers


  • Re: What goes through the Fuse box?

    by » one month ago


    Rotax Wizard,

    Thank you for your time in explaining all of this.

    I guess my confusion came from not being able to find a wire carrying +5 volts coming out of the fuse box going to the ECU. I do find several wires coming out of the ECU that have +5 V going directly to the sensors. I made the assumption that the power that ultimately comes from the generators, thru the voltage regulators to the fuse box and then to the ECU was a single voltage (whatever that is from the voltage regulators, 13.8V?) and the ECU had the facilities (a power supply of some sort) to provide the required +5V to the sensors.

    Thanks again for setting me straight.

    Ray


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