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  1. #1

    Default why two sensors on detroit 6-71 fuel filter?

    I have a detroit diesel 6-71 and I'm wondering why this engine has two different sensor on the fuel filter.
    I've attached a foto showing these two sensors, so if anyone knows what these sensors are used for, I would appreciate it.
    jimClick image for larger version. 

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  2. #2
    Join Date
    Nov 2009
    temecula, ca., usa

    Default Re: why two sensors on detroit 6-71 fuel filter?

    Well, this is just guessing but they usually use pressure "sensors" or switches like these to either ENABLE or DISABLE a circuit. Usually by altering the circuits ground state after fuel pressure builds.

    On the one in the picture that I can clearly see, it only has a single wire going to it so it is either supplying a ground for something or is taking a ground away depending upon if it is a NORMALLY OPEN switch or a NORMALLY CLOSED switch.

    Pressure is also a factor. These switches can open or close as low as 2 psi on up to 25 or even 50 psi.

    For instance: If it were a NORMALLY CLOSED pressure switch, then it could be utilized to take the ground off of a starter relay thereby not allowing the starter to engage after the fuel pressure reached, say 15 psi. This is a nice feature in that it keeps the operator from accidentally engaging the starter while the engine is running and damaging the starter and flywheel.

    In order to establish EXACTLY what these are intended to do, guy would need to:

    1. Identify if it is a normally open or normally closed switch...easy with an ohmmeter.

    2. Determine the pressure value at which the switch opens or closes...usually stamped on the switch under all that Detroit green spray paint.

    3. Trace the wiring from the switch to it's terminal point...easy or hard depending on the size of the vessel and extent of the electrical system.

  3. #3

    Default Re: why two sensors on detroit 6-71 fuel filter?

    thank you jgmo.
    You've given me a place to start.
    I will use your suggestions to try to figure out how these sending units function.

  4. #4

    Default Re: why two sensors on detroit 6-71 fuel filter?

    Did you ever figure out what the sensor does?

  5. #5

    Default Re: why two sensors on detroit 6-71 fuel filter?

    long shot since it was so long ago but did you ever find info on the pressure switches? I have a similar situation and can find no information regarding sensor pressure settings. I have one leaking fuel so I sort of need to replace it LOL

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