MGL Avionics User Forum

Fuel level sender won’t calibrate to empty
Checking and correctly setting all the selections and dip switches has cleared all but two of my set up puzzles.
I still have not solved one of the fuel level senders reading incorrectly... By process of elimination what the problem is not is, wiring, grounding, the sender it' s self or settings.
Both tank 1 and 2 are setup the same in the setting menus.
The tank two reads nearly full but has no fuel in the tank. Tank one reads correctly. Nearly empty.
Grounding. The RDAC is grounded directly by way of the two ground point hookups to one of four of the unused vacuum pump pad lugs on the engine. All the various sender grounds go to this location. The engine is grounded to the engine mount via a bond strap from engine to welded lug on the mount. The ground wire from the RDAC harness is run to a dedicated avonics ground bus, that bus is grounded via a 14 gauge wire directly to the battery ground lug, which is attached to a welded lug. The aircraft has three separate ground busses. Avionics, Lighting, General. Each have their own home run wires to the battery ground. Each are on the port side if the AC, with power run on the starboard side.
I'm pretty sure grounding is not the issue.
I calibrated a new fuel sender to zero per the calibration instructions. With the jumper in place the reading goes to empty, remove the jumper and it goes back to near full
I checked resistance on both tanks senders ground wire and send wires and got almost identical readings from both tanks.
I'm sure it's not a broken wire or bad molex connector at the wing root.

I'm stumped.

DEW

It sounds like you are not actually calibrating the fuel level system in the EFIS itself ?
The mention of a jumper has me confused here.

You must calibrate using the 6 point linearization system for each tank. For each tank it displays in the calibration function the "raw" reading. This is a number form 0 to 4095 which corresponds to the voltage it measures on the fuel level sender inputs.

If you have an external calibration system (like you tend to have with electronic probes) this must be calibrated first so that you fall in with the above number range. It does not matter if the number increases or decreases with level - as long as there is a good and reliable change.

Thanks Rainier
Sorry about the confusion reg the jumper. The jumper was in reference to zeroing out the sender per the sender instruction.
Because tank 1 read 0005 at empty I assumed that tank 2 should have started with something like the same value in the linearization system.
I've adjusted tank 2 to start empty with a reading of 248 and have set the next points in 50 unit intervals matching tank 1 and will adjust as I go while filling the tanks.

On the bright side, I've now completed a really through check of all my grounding

Thanks DEW