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Electric fuel pressure gauge

in General Tech Discussion 8 years ago

  • Re: Electric fuel pressure gauge

    by » 5 years ago

    Bill,
    No shield. Here is the pin out for the expensive precision German ROAD harness for connection from the sensor to their fuel pressure gauge. Black is + (power), Green is Sensor (.05 - 4.5VDC voltage input to the gauge from the sensor), and Red is ground. I’m Not making this up. Verified this at the gauge. There is a fourth (yellow) wire in the “three wire” harness that has no continuity to anything else in the harness. At least on the harness I received from Aircraft Spruce. Using a 1.5V AA battery rig I finally determined the the gauge is fine, the problem is with the never flown $147 sensor. Peeking inside, I see that the sensor chamber piston that should move in and out with fuel pressure is jammed full in and thus the sensor is continuously transmitting the full 4.5V to the gauge, My attempts to free it bore no fruit. So despite the fact there’s no fuel pressure at the manifold, the gauge reads max pressure. I spoke with Aircraft Spruce and requested a no cost replacement (fingers crossed) and a chance to speak with anyone from ROAD but I doubt anything will some of that. ROAD is in Deutschland and to date they’ve ignored my independent email inquiries.
      
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  • Re: Electric fuel pressure gauge

    by » 5 years ago

    ... Black is + (power), ... and Red is ground. I’m Not making this up...


    I don't mean to question your results. ... OK, Yes I do! :)
    Did you remember that the picture was of the Sensor and so the Connector/Harness is going to be a mirror image that reverses the Black and Red? Red= Power. Black = Ground. ???

    Just checking because I can't see what you see.

    I am surprised that you took the sensor apart.
    I am also surprised that there is a moving piston!
    I would have assumed it was a strain gauge with No moving parts.
    Are you sure you're sure?

    Seeing how you have already decided the sender is scrap.
    Try reversing the Red and Black power leads from the Sender. RED(+) BLK(-)
    You have nothing to lose.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Jim Isaacs
      
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  • Re: Electric fuel pressure gauge

    by » 5 years ago

    Bill
    No worries! I appreciate your feedback and don’t mind you questioning my troubleshooting at all. At one point I had the sensor on my lap, plugged into the harness, as I sat in the aircraft. I had the gauge out of the instrument panel but connected to aircraft bus power and the aircraft ground bus. Using the unterminated gauge harness wires as test leads, I had the black harness wire connected to the gauge + terminal, the red harness wire connected to the gauge - terminal, but no other harness wires touching the gauge. I then put 1.5V directly to the gauge S terminal (bypassing the harness) using the AA battery I rigged, and for the first time, the gauge indicated a PSI less than pegged beyond max. At that point I put my multimeter test leads on the Green harness sensor output wire and aircraft ground, and I saw 5 volts on my meter. The max output to the gauge should be 4.5v. I will try reversing the power and ground wires to the sensor and measure the output from the sensor.
      
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  • Re: Electric fuel pressure gauge

    by » 5 years ago

    Bill
    Yup you were correct I had the red and black wires reversed. Unfortunately it made no difference, the sender is locked down on sending 5VDC and still pegs the gauge at max psi despite the fact there is no pressure at the manifold.
      
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  • Re: Electric fuel pressure gauge

    by » 5 years ago

    Well the “three wire” harness arrived and just to make things sportier for me, it has three female pins at the sensor end- and four wires peeking out from the sheathing at the gauge end.


    That makes sense per your previous post. three wires at the sender and a fourth at the gauge for the night light.
      
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