fuel sender

[HansLab]

All, some time ago I calibrated my tank/EFIS combination. Long time no action on that front, until I try to get the fuel system leak free to test the engine.
Now I put 20 liters fuel in the tank - and the EFIS says the tank stays empty.
What could I have forgotten? And how can I test the sender - without taking it out of the tank?
By the way I have a MGL set EFIS and assecoires.

 

[Mich48041]

The most likely cause of the problem is poor grounding of the fuel level sensor steel mounting plate. With EFIS turned on, measure the voltage between the airframe and the fuel level sensor steel mounting plate. If the voltage is not zero, fix the poor ground.
Testing the sensor:
With electrical power turned off, measure the resistance of the sender between the center screw and the steel mounting plate. It should be between 25 and 260 ohms, depending on the fuel level.

 

[DHeal]

Early kits assumed that the steel fuel sensor mounting plate would be adequately grounded through the aluminum fuel tank itself (i.e., a one-wire installation). This did not prove true in all cases. Many of us added a second dedicated ground wire from the steel fuel sensor mounting plate to a nearby airframe grounded connection.

 

[HansLab]

ground

Thanks, it has to be something like that! I'll add a second ground wire and let you know. Now I have ohms to measure I can get some kind of hold on this process. Thanks all of ya.

 

[RFSchaller]

Did you bend the float wire so that the float touches the tank bottom when it hits the mechanical stop? Mine touches the tank bottom when it hits the lower stop, so it hits the upper mechanical stop at 17 gallons. I usually fly a full tank 1 hour before it starts to register level at 16 gallons. When I bent the float wire I decided it was better to know if I have 3 gallons or 0 as opposed to 17 or 20.

 

[HansLab]

Helaas; tried the Ground-trick today: no luck. Tried several places on the plate, even ran a wire to the battery-negative: nothing.
Thought of it to measure the Ohms though: 127 (20 liter). Should be between 240 and 33 Ohms.
it looks like the float isn't stuck. Next week I'll pull the RDAC plug for all certainty, and if that doesn't give a solution I'll dismantle the sender.

Up & downs, this experimental building.
The good news is that I was able to install the washers on the HS today, and was able to dismount the avionics bay, despite an unreachable screw ;-)
Life's good.

 

[Mich48041]

Measure the voltage between airframe ground and the fuel level sender center screw.
What is that voltage?

 

[Piper J3]

My early S/N RV-12 with D-180 got corrupted fuel sender memory. I had to recalibrate by emptying tank and adding 2 gal increments. Been working fine since...