Fuel Level redux

[FlyPig]

I've searched the forums and followed whatever troubleshooting advice I found but I'm sending out a final SOS before I begin the arduous process of tank removal and sensor replacement.

The capacitive senders never worked, so I replaced them with mechanical float-type a decade ago. I believe both sides worked (but can't remember) until I sent the left one off to WEEPNOMORE. I'm pretty sure this is where my current frustrations began.

After many years of just topping up the left tank every time and running it dry, I'm finally fed up looking at "CAL" in the Dynon D180 display for the left tank. I follow the calibration procedure and after I've added the first 2 gallons, the D180 doesn't sense anything (retains an initial value of 500) and asks if I'm sure. I hit YES and do another 2 gallons, same result, +2 gallons...same. Abort calibration.

I replaced the wire from the sender to pin 20 on my D180. The sender flange was already grounded all the way to my firewall ground block years ago with an initial futile attempt at solving the problem but (in my madness) just in case, I ran a ground from a different screw on the sender flange to a bolt on the fuselage. Same problem calibrating. Ohmeter reads 0 between sender flange and fuselage bolt.

While draining those 6 gallons, I put the Ohmmeter between the sender center electrode and the flange (or the airframe -- same outcome) and observe the following readings:

6 gal 3550 (M ohm?)
5 gal 3490
4 gal 3475
3 gal 3460
2 gal 3445
1 gal 3432

Do these make sense, or could I be hoping what I'm seeing is float movement? To be clear, the D180 value stays at 500 throughout.

For good measure I went to the D180 d-sub connector and swapped fuel sender wires for the left and right tanks. Calibration through the left channel of the right tank (now holding about 16 gallons) yields an initial value of 75 versus the 500 value I now see through the right D180 channel (and originally through the left). So, the problem follows the actual tank sender.

NOW, before I inflame carpal tunnel removing those **** fuel tank attach bolts AGAIN to get to the fuel sender, what other low-hanging fruit have I missed.

Thank you, Braintrust!

 

[rv8ch]

I've searched the forums and followed whatever troubleshooting advice I found but I'm sending out a final SOS before I begin the arduous process of tank removal and sensor replacement.

The capacitive senders never worked, so I replaced them with mechanical float-type a decade ago. I believe both sides worked (but can't remember) until I sent the left one off to WEEPNOMORE. I'm pretty sure this is where my current frustrations began.

After many years of just topping up the left tank every time and running it dry, I'm finally fed up looking at "CAL" in the Dynon D180 display for the left tank. I follow the calibration procedure and after I've added the first 2 gallons, the D180 doesn't sense anything (retains an initial value of 500) and asks if I'm sure. I hit YES and do another 2 gallons, same result, +2 gallons...same. Abort calibration.

I replaced the wire from the sender to pin 20 on my D180. The sender flange was already grounded all the way to my firewall ground block years ago with an initial futile attempt at solving the problem but (in my madness) just in case, I ran a ground from a different screw on the sender flange to a bolt on the fuselage. Same problem calibrating. Ohmeter reads 0 between sender flange and fuselage bolt.

While draining those 6 gallons, I put the Ohmmeter between the sender center electrode and the flange (or the airframe -- same outcome) and observe the following readings:

6 gal 3550 (M ohm?)
5 gal 3490
4 gal 3475
3 gal 3460
2 gal 3445
1 gal 3432

Do these make sense, or could I be hoping what I'm seeing is float movement? To be clear, the D180 value stays at 500 throughout.

For good measure I went to the D180 d-sub connector and swapped fuel sender wires for the left and right tanks. Calibration through the left channel of the right tank (now holding about 16 gallons) yields an initial value of 75 versus the 500 value I now see through the right D180 channel (and originally through the left). So, the problem follows the actual tank sender.

NOW, before I inflame carpal tunnel removing those **** fuel tank attach bolts AGAIN to get to the fuel sender, what other low-hanging fruit have I missed.

Thank you, Braintrust!

Couple of questions and a comment. Have you checked the resistance on the other sender? Have you tried adding more fuel? 6 gallons is not much and may not be enough to allow the "float" to float.

 

[Mikeyb]

From my notes: The standard Vans SW tank level sensors measure about 30 ohms full and 250 ohms empty.

 

[Carl Froehlich]

Run a ground wire from the base of the float sender (under a screw head) to ground.

Carl

 

[Kyle Boatright]

Run a ground wire from the base of the float sender (under a screw head) to ground.

Carl

Use a set of alligator clips to accomplish this first. Clamp to the screw, then to another airframe part. If you find that's the issue, go to the permanent solution as suggested by Carl.

If that doesn't work, use a multimeter to check the sender's resistance at full and empty to see what range of resistance it is giving you. The sender could be stuck. The float could have come off, the wire could have come loose, maybe the float sank, etc. Your first indication of any of those things would be no change in resistance between known full and known empty.

 

[Webb]

Vans techinical help told me to put a star washer under a screw for both the sending unit and the panel cover.

 

[lr172]

While draining those 6 gallons, I put the Ohmmeter between the sender center electrode and the flange (or the airframe -- same outcome) and observe the following readings:

6 gal 3550 (M ohm?)
5 gal 3490
4 gal 3475
3 gal 3460
2 gal 3445
1 gal 3432

Do these make sense, or could I be hoping what I'm seeing is float movement? To be clear, the D180 value stays at 500 throughout.

The typical stewart warner floats should read from 30-330 ohms or close to that; memory a bit fuzzy. You may not get the full range. but any readings outside of that range indicate that they are not working. No surprise if someone was sloshing around a liquid sealant in the tank. It is just a wiper across a set of carbon traces (like a potentiometer) and it is not covered with anything. It is fully exposed and any sealant that got on the carbon traces will create very high resistance like you are seeing. Shame on the slosh guy as he should know better and removed them before sloshing.

the variable resistance as the arm moves, shows that you are getting reliable indications from the meter IMHO. The senders ground source is the flange and that is where the probe was placed, so no star washer required to get a good test reading.

Larry