jjconstant
Well Known Member
I'm hoping to get ideas on how my left fuel indication failed. The symptom was that the indication would read correctly for a long time and then start to sweep from correct to -10 gallons, randomly and finally only reading -10.
-10 is also the indication you get when there is either no ground or no signal from the sender. This behaviour would happen both in flight and stationary on the ground with no movement at all.
I did what troubleshooting I could and concluded that the sender (float type) had to be bad so I pulled it out of the tank and indeed it was bad. The wire was broken at the big blob of solder going from the swinging arm mechanism into the base/back of the hole you screw the wire into that then goes to the instrument. I must have over tightened the screw. The failure behaviour lead me to believe that the broken wire would variably be connected and then open or very high resistance.
I thought this would solve the problem but, after thinking it was fixed and reading correctly, it started back to the old failure of variable between correct and -10. I redid all the troubleshooting including checking the resistance of the entire harness wire from the instrument all the way to the connector at the tank. Everything was O.K. Out of desperation, I stripped enough insulation from around the 470ohm resistor to put test leads on each side of it. It ready correctly. For about 5 minutes. Then it started varying wildly. O.K...bad sender AND bad resistor. I cut out the resistor and soldered in a new one, again being VERY careful not to put much heat into the resistor. It now reads correctly. For now.
I have now been away for a day or two. I'm going back to recalibrate the tank (different sender) but want to be prepared for it to start not working again. Could the wire breaking at the sender have caused the resitor to fail? Should I be looking elsewhere for something to have caused the resistor to fail? I must say that having a broken wire in the fuel tank has given me pause...is there enough current to cause a fire if the tank were almost empty?
Thanks
Jeremy
-10 is also the indication you get when there is either no ground or no signal from the sender. This behaviour would happen both in flight and stationary on the ground with no movement at all.
I did what troubleshooting I could and concluded that the sender (float type) had to be bad so I pulled it out of the tank and indeed it was bad. The wire was broken at the big blob of solder going from the swinging arm mechanism into the base/back of the hole you screw the wire into that then goes to the instrument. I must have over tightened the screw. The failure behaviour lead me to believe that the broken wire would variably be connected and then open or very high resistance.
I thought this would solve the problem but, after thinking it was fixed and reading correctly, it started back to the old failure of variable between correct and -10. I redid all the troubleshooting including checking the resistance of the entire harness wire from the instrument all the way to the connector at the tank. Everything was O.K. Out of desperation, I stripped enough insulation from around the 470ohm resistor to put test leads on each side of it. It ready correctly. For about 5 minutes. Then it started varying wildly. O.K...bad sender AND bad resistor. I cut out the resistor and soldered in a new one, again being VERY careful not to put much heat into the resistor. It now reads correctly. For now.
I have now been away for a day or two. I'm going back to recalibrate the tank (different sender) but want to be prepared for it to start not working again. Could the wire breaking at the sender have caused the resitor to fail? Should I be looking elsewhere for something to have caused the resistor to fail? I must say that having a broken wire in the fuel tank has given me pause...is there enough current to cause a fire if the tank were almost empty?
Thanks
Jeremy