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Old 01-06-2022, 07:28 PM
N29945 N29945 is offline
Join Date: Dec 2020
Location: Mineola TX
Posts: 33
Default Empty fuel indication

I have an RV6A that I recently purchased, the left fuel indicator indicates empty, irregardless of the quantity of fuel in the tank, the airplane first flew in 2005 so my suspension is a fuel indicator transmitter problem, I have replaced the indicator with a new old stock gauge and the indications are exactly the same, it is time for my first condition inspection, any ideas on troubleshooting the sending unit, and do I have to remove the tank to troubleshoot it?
Thank you

Jim Skinner
Exempt but a privilege to donate in 2022
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Old 01-06-2022, 07:47 PM
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Vlad Vlad is offline
Join Date: Oct 2008
Location: Utah
Posts: 8,527
Default Sender removal and replacement

Jim you can get the sending unit out without removing the tank. Take your time you will use a lot of words but very few tools . I recently discovered a leak from a sending unit took me couple hours to get it out. In a freezing cold of course...
Не имей сто рублей, а имей сто друзей.
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Old 01-06-2022, 08:25 PM
RV10Pilot RV10Pilot is offline
Join Date: Jan 2005
Location: Medford, NJ USA
Posts: 519

Bad ground of the sensor? Post 3 here

I will assume they are float type sensors. The float sender is basically a variable resistor. The higher the float is the less resistance the sender will provide to make the gauge read fuller. Measure the resistance when there is a little fuel in the tank, fill the tank and measure the resistance. The resistance should change. You measure the resistance from the post on the sending unit and ground.

The wire could be bad. Measure continuity from the sender to the indicator.
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Old 01-06-2022, 10:10 PM
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rvbuilder2002 rvbuilder2002 is offline
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,790

I agree. The sender should only be removed after troubleshooting has been done and it is confirmed to be bad. The way the system works is the indicator reads empty with the highest resistance of the sending unit. So any amount of resistance more than 240 ohms will make the indicator read empty (Full reading is about 30 ohms). A broken sender wire or a bad ground path for the sender would make the resistance more than 240 ohms…
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Old 01-06-2022, 10:40 PM
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tom paul tom paul is offline
Join Date: Aug 2017
Location: Brooklyn
Posts: 41
Default Mine has issues too

My 7A fuel gauges don't always indicate fuel, or one will and the other won't. I asked the guy I bought it from and he just said, "yeah, it does that. Just cycle the master and they might come on" Welp, that's what I do, and they always do, but sometimes one goes off, and the other comes on. I sometimes have to cycle the master two or three times to get them both indicating.
Not comforting, but I measure my fuel by sight, fuel hawk, and hobbs meter, so I am OK with it. Unless it points to other issues I should be worried about.
3rd owner, bought flying
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Old 01-07-2022, 12:06 AM
gasman gasman is offline
Join Date: Mar 2007
Location: Sonoma County
Posts: 4,337

Sounds like the gauges are reading resistance in the master solenoid... dirty contacts.

Why don't you try running a temporary dedicated power wire to your fuel gauges and see if they stabilize.
Bypass the master solenoid with a fused wire right from the battery.
VAF #897 Warren Moretti
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Old 01-07-2022, 12:26 AM
danny danny is offline
Join Date: Jul 2005
Location: puyallup, wa
Posts: 169
Default Quick check

I had the same problem on my right tank. I pulled the wire at the sending screw...and attached one end of a jumper wire to ground and the other to the detached wire. The gauge went to full and a new sending unit fixed the problem. I keep several lengths of wire with different ends and alligator clips in a jar just for troubleshooting things like this.
Start with the low hanging fruit first.
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Old 01-07-2022, 12:56 AM
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rv8ch rv8ch is offline
Join Date: Feb 2005
Location: LSGY
Posts: 4,628

During your CI you will remove the fairings between the wing and the fuselage, and under there you will see the fuel level sensor. It will looks something like this:

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Set your multimeter to Ohms and touch the screw and a good ground, and see what values you see. If you can make those numbers change by sloshing around the tanks, that means that the fuel level sensor is probably working ok. As mentioned earlier, there is a range of resistance that it should show on your multimeter.

If it reads ok, perhaps the ring terminal on the wire is a bit corroded, or the wire might be broken. Also check the ground wire which should be nearby.

Good luck!
Mickey Coggins
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Old 01-07-2022, 06:34 AM
Southern Pete Southern Pete is offline
Join Date: Jul 2015
Location: England
Posts: 158

If a new ground wire will solve the problem then happy days.
The level of difficulty in replacing the sender unit depends very much on how the tank was built. I've done 3 in the last couple of years. One was particularly time consuming where the original builder had used nylocs inside the tank and a lot of sealant. The whole access panel had to come off by cutting the proseal. The sender should be sat on a bed of proseal, you may have to cut that with a thin blade to remove the old item. Clean up is with MEK.

Removing the tank is not so difficult, particularly on a 6. If you have any doubts about doing it in situ I would pull the tank without another thought. Build a cradle to hold the tank once it is off.

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Old 01-07-2022, 07:03 AM
WingsOnWheels WingsOnWheels is offline
Join Date: Mar 2009
Location: Plano, TX
Posts: 2,292

Originally Posted by Vlad View Post
Jim you can get the sending unit out without removing the tank. Take your time you will use a lot of words but very few tools . I recently discovered a leak from a sending unit took me couple hours to get it out. In a freezing cold of course...
Vlad, Just to note, on the 6 it is much easier to remove the tank than on the later models. I can pull a tank in about 15min. Much easier to work on that way especially since there is less room to work (smaller gap from fuselage to tank) on the 6 as well.
Colin P.
RV-6A #20603
Complete 5/10/19
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