I need help understanding/troubleshooting fuel level sensor.

[jcarne]

Hello everyone!

I have the Dynon HDX in an RV-7A. Lately my left tank fuel sensor has not been working (reads zero, occasionally shows a fuel quantity but mostly just zero). It does usually work to some degree when tanks get to below half. If it is full it almost always shows 0 gal. It was working once upon a time and seemed to get more problematic as time progressed. The aircraft has only been flying since March. The picture below is an example of how sporadic it can be.

I have done a re-calibration and the values all look good/ comparable to the right side. Max voltage was 3 (at empty) and min was around 1.2 (full) if memory serves. However, right now for voltage it shows 5V in the sensor debug menu. If I tap the tank in the area of the sensor I can get the voltage to change very very slightly. Any idea what may be causing this/ where I should focus attention?

The real kicker, my left tank sender is in the second bay, so pulling it would involve pulling the tank... I'm looking to really understand the issue (and how the voltage relates to reading the sensor) as best I can before going down that road.

Thanks for your help!

 

[jdubner]

A 5V indication would imply no sender is connected. Remember, the sender is two connections: signal and ground.

Using the standard Van's fuel tank senders? They're notorious for making a poor connection to airframe ground through the tank sealant or whatever you used to install them.

II used a short wire to positively ground the sender (picture below).

--
Joe
RV-8A
Independence, OR

 

[jcarne]

Yep this is a standard Van’s sender. When I installed it I took extra special care to ensure there was a good ground path through the screws. I metered it and ohm checked it. All worked great on installation which is why I’m confused this would just pop up like it has.

 

[pacecapt]

Why is it that we have had very accurate fuel senders in auto for years yet they can't seem to get that technology into our E-AB's???

 

[Stevec]

i had exactly the same issue. All working well one day then the next fuel level zero. After experimenting with a bent stick in the filler hole I found the sender had developed a dead spot mid range so no amount of re calibrating would have fixed it. Replaced the sender with a new one and all well.

 

[jakej]

Why is it that we have had very accurate fuel senders in auto for years yet they can't seem to get that technology into our E-AB's???

Happens in GA aircraft too - had a Navajo in doing a fuel cal & bought 8 new Pma'd float sensors - everyone of them had to be 'adjusted' to make them work linearly correctly

 

[jcarne]

i had exactly the same issue. All working well one day then the next fuel level zero. After experimenting with a bent stick in the filler hole I found the sender had developed a dead spot mid range so no amount of re calibrating would have fixed it. Replaced the sender with a new one and all well.

Steve you may be on to something.

Just to update everyone on a new finding. Anytime I fill up it shows zero. In fact it always shows zero until I have about 5-6 gallons left in the tank. When the fuel level drops to this amount it works perfectly every-time. Sooooo... looks like I get to pull this piece of garbage and put in a new one. Not something I am happy about as I have to pull the whole tank. It wouldn't bother me except for the fact it's a requirement for IFR flight and I want to finish my instrument ticket.