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Testing Resistive fuel sending units

L

litewings

Active Member
Have a -0- fuel indication on a a RV8 with standard Vans sending units. Anyone know what the resistance should be from full to empty? Graeter resistance while in the full position or empty position? Hopefully something that can be checked with a ohmmeter.
 
The senders tend to be about 10 to 300 ohms. If it reads a dead short to ground (0 ohms) or above about 500 ohms, you have an issue. They should read lower with higher resistance, so zero fuel sounds like high resistance.
 
I had a fuel sender that initially did not work because I was too good with the proseal, and it was insulated from the airframe. Solved by adding a star washer under one screw head. Check to see if you have continuity from the sender body to the airframe.
 
aturner said:
I had a fuel sender that initially did not work because I was too good with the proseal, and it was insulated from the airframe. Solved by adding a star washer under one screw head. Check to see if you have continuity from the sender body to the airframe.
Click to expand...

Andy is correct
This is the most common problem
 
I'm not sure what type of sending units the original builder installed in my RV-8. My issue is that the left tank either indicates empty, or some level which appears to be an accurate based on visual inspection/time feeding from tank. There is a single wire that leads from *somewhere behind the tank* then into the fuselage. The right tank looks to be indicating properly. This has always been an issue with the plane since I've owned it, not something that just started. Questions:

How can I tell if this is a capacitance vs. resistive system?
What type of problem does this type of intermittent behavior indicate?
How should I test the system?

Thanks!

CA
 
I measured the fuel float sender yesterday for the RV-3B tanks I'm building. This was for the right tank, the left tank isn't quite ready to test yet.

Full was 31 ohms. Empty was 241 ohms.

Dave
 
Be careful tightening the screw for the wire to the gague. It is very easy to overtighten and it will break the wire on the tank side of the sender, resulting in either intermittent problems or zero gallon reading. The only solution then is to remove and either replace the sender or re solder the wire.
 
maus92 said:
I'm not sure what type of sending units the original builder installed in my RV-8. My issue is that the left tank either indicates empty, or some level which appears to be an accurate based on visual inspection/time feeding from tank. There is a single wire that leads from *somewhere behind the tank* then into the fuselage. The right tank looks to be indicating properly. This has always been an issue with the plane since I've owned it, not something that just started. Questions:

How can I tell if this is a capacitance vs. resistive system?
What type of problem does this type of intermittent behavior indicate?
How should I test the system?

Thanks!

CA
Click to expand...

If you have a single wire going somewhere behind the tank then you probably have a standard float type sender mounted in the rear baffle of the second rib bay outboard, to allow for a flop tube in the first bay. The most common cause of your symptom is a poor ground connection between the flange of the sender and airframe ground.
 
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