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Fuel tank sender

DeltaVee47

Active Member
I know this problem has been beat to death but I can?t find my answer in the files.
So I have the Vans supplied resistive float fuel senders hooked up to G3X.
I get 1.007V on L and 1.223V on right when I start the calibration per the G3X manual. Add 5 and 10 gal fuel, no change in voltage. I have tried all the tricks such as recommended by Scott and others without success. Good grounding both sides so far as I can tell with my meter. So I?m about down to pulling the units to see with my own eyes how I screwed up the install.
My question is can I do this without pulling the wings and any hints/tips greatly appreciated.

Thanks everyone
Greg Beckner
N557GB
140366
 
Make very sure you have the pins right in the GEA24. And you can measure the resistance of the sender to ground with the wires unplugged from the GEA24. If you check with it plugged in you are also measuring the path through the box and that is distracting.
 
What the above poster said and we can simplifier even more by checking the resistance right at the sender. If you see resistance change at the sender, then the problem is on the wiring from the sender to the GEA24
 
Yes - I did mean to check at the sender, just make sure the plug is off at the avionics side of the equation. Then you can also check the wire continuity at the plug. Keeps you from unscrewing/rescrewing the sender wire if you don't have to.

Should check resistance from sender terminal to shell of sender first. Then terminal to wing aluminum. Then plug pin to wing. Then plug pin to battery or ground tabs (the ultimate ground). Don't assume the ground from the sender to the wing and the wing to the fuse and the fuse to the battery is good unless it is all tied in.

Personally, I got the L and R backwards not knowing which Garmin called #1 and #2. Swapped the pins and was in business. Couldn't understand why gas in the left tank didn't change the reading - turns out it was changing the right side just fine!
 
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The standard kit supplied sensors have a resistance range from about 240 ohms empty, to about 30 ohms at full, when measured relative to airframe ground.
 
I get 1.007V on L and 1.223V on right when I start the calibration per the G3X manual.

Did both of your floats have the 16th clearance top and bottom when you were fitting the wire?

If one of them has bottomed out it would explain your readings.
 
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These are all things I have not checked but will do tomorrow when at the hanger. Its only about 125 degrees in there this summer. Houston is the best.

Greg Beckner
n557GB
 
Just about everybody I know who is or has built a 14 had to put an extra bend in those wires to keep the senders from touching the top and/or bottom of the tank, ymmv.
 
If one of them has bottomed out it would explain your readings.

Just curious about the logic on this?

We are reading the resistance and calculating based on that resistance. If the float is touching the bottom, then wouldn't this just be the resistance value the start of your empty tank. Granted, since it is a bit further away from the inboard area, one could still have a bit of gas in the tank and still read zero but that amount is even more with the 1/16th off the bottom.
 
If the float is touching the bottom, then wouldn't this just be the resistance value the start of your empty tank.

Yes, but since those two wires are probably not perfectly bent at the same angles if they are bottoming out it will show different resistance.

Probably one of the reasons for the 16th clearance on the tops and bottoms of the floats is so the sensor bottoms out before the floats hit the skins.
 
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Yes, but since those two wires are probably not perfectly bent at the same angles if they are bottoming out it will show different resistance.

Probably one of the reasons for the 16th (double check for the exact clearance, from memory) clearance on the tops and bottoms of the floats is so the sensor bottoms out before the floats hit the skins.

The resistance is so sensitive that probably do not read the same even uninstalled, mine were slightly different when I checked them before installation. But also we calibrate each tank independently, so they do not need to read the same resistance unless one was going to set the fuel value purely based on a pre set value of voltage instead of adding X gallon of fuel at the time and then setting the value.
 
The resistance is so sensitive that probably do not read the same even uninstalled

Observed this as well and did calibrate the tanks separately. Also it takes longer for the gauge to start reading on a full tank, once it gets down to 2/3 it starts moving quite liberally. Probably the shape of the tank.
 
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