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G3X Fuel Level Problem

Kyle Boatright

Well Known Member
The issue is that there is little or no discrimination on my fuel gauges from empty to full. I have the G3X set for resistance senders, and see little or no voltage difference between voltage levels when the tanks are empty, hold 5, 10, 15, 20, 25 or 30 gallons. I've temporarily wired in a known good S/W sender so I can move the arm up and down while in the cockpit to see what impact moving the float arm has on the voltage drop according to the G3X. Basically nada.

On the other hand, when I use a multimeter to check resistance through the sender itself, the resistance varies by a factor of 10 as I move the arm through its arc.

My request is for someone who's flying a G3X with the S/W senders to take a screenshot or publish the voltage values from the calibration page. I'd like to get a sense of how much voltage drop there is at various fuel levels, so I can recognize reasonable readings when I eventually get them.

P.S. When I spoke with one of the the G3Xperts, he opined that it is a wiring issue. I'm dreading the possibility I have to pull the engine sensor wiring harness. That's a bad job.
 
This is my data from a RV-14 fuel tank with stock senders and a G3X
 

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Thanks, Glenn. My input voltages are in the range of 11.9, so there's a big disconnect there.

Did you use shielded cable to the senders? Any chance that you inadvertently crimped any of the shielding?

Perhaps check resistance further upstream at your connection at the panel.
 
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Did you use shielded cable to the senders? Any chance that you inadvertently crimped any of the shielding?

Perhaps check resistance further upstream at your connection at the panel.

Professionally made harness, so I can't speak to any shield/crimping issues.

I don't understand your comment about checking resistance upstream. Where, specifically?
 
I'm probably not the best person to help with trouble shooting. Senders supplied by Vans are 30 to 240 ohms. This could be checked at the sender but also at the other end of the wire where it connects to the Garmin GEA-24, I'm going from memory. This would confirm proper continuity from the sender to the connection at the panel.

If the harness was professionally built perhaps reach out to them.
 
I'm probably not the best person to help with trouble shooting. Senders supplied by Vans are 30 to 240 ohms. This could be checked at the sender but also at the other end of the wire where it connects to the Garmin GEA-24, I'm going from memory. This would confirm proper continuity from the sender to the connection at the panel.

If the harness was professionally built perhaps reach out to them.

The sender checks out, so either there's a wiring or a configuration issue. And yes, I've been in touch with the shop that built the harness. Their best guy has been out of town, but will be back Monday. I was hoping for an "aha" moment so I could resolve the issue tomorrow, but that seems less and less likely...
 
11.9v

11.9 volts suggests you have them wired as per the top option and have a bunch of resistance towards the sensor.

Also means your config should be set to voltage rather than resistive which might be counter intuitive.

Otherwise I'd start looking for where that 12v is coming from.

Derek
 

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11.9 volts suggests you have them wired as per the top option and have a bunch of resistance towards the sensor.

Also means your config should be set to voltage rather than resistive which might be counter intuitive.

Otherwise I'd start looking for where that 12v is coming from.

Derek

Mine is wired like the bottom examples above and I get voltages around 1 or 2, but can't really remember as I haven't looked in a long time. Getting readings of 11 makes me think that something either not wired right or the config doesn't match the wiring scheme.
 
The issue is that there is little or no discrimination on my fuel gauges from empty to full. I have the G3X set for resistance senders, and see little or no voltage difference between voltage levels when the tanks are empty, hold 5, 10, 15, 20, 25 or 30 gallons. I've temporarily wired in a known good S/W sender so I can move the arm up and down while in the cockpit to see what impact moving the float arm has on the voltage drop according to the G3X. Basically nada.

On the other hand, when I use a multimeter to check resistance through the sender itself, the resistance varies by a factor of 10 as I move the arm through its arc.

My request is for someone who's flying a G3X with the S/W senders to take a screenshot or publish the voltage values from the calibration page. I'd like to get a sense of how much voltage drop there is at various fuel levels, so I can recognize reasonable readings when I eventually get them.

P.S. When I spoke with one of the the G3Xperts, he opined that it is a wiring issue. I'm dreading the possibility I have to pull the engine sensor wiring harness. That's a bad job.
Kyle,

11.8 Vdc is the open circuit voltage for the system when a resistive fuel quantity sensor is selected.

This voltage is presented on the calibration screen when either the resistive fuel quantity sensor is not grounded (at the top of the sensor), or when GEA 24 connector P244, pin 6 is not connected to anything for Fuel Qty 1.

It does indeed sound like a wiring error. Just run a wire from GEA 24 connector P244, pin 6 to your known good test sensor making sure that your test sensor is properly grounded and you should see it work fine.

The resistive fuel quantity sensor that Van's uses operate between approximately 20-240 ohms. When the tanks are full the resistance is approximately 20 ohms, when empty the resistance is approximately 240 ohms. I saw 0.210V at 22 ohms and 2.434V at 220 ohms.

Steve
 
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As suggested by several people who posted in the thread, it was a wiring issue.

The folks who made the harness used a shielded 3 wire bundle to go out to the tank.

Anyway, they mislabeled the sender wire (shoulda been the orange/white, not the white/white). Problem corrected. (After I spent 10 hours and a couple of quarts of sweat chasing the problem and applying incorrect fixes.)
 
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