Fuel sender unit

I'm helping a friend diagnose a fuel sender problem that he has with both units. Both units were calibrated to his afs efis and worked fine. One quit showing anything early onto phase 1 and the second quit a few hr later.

We removed the sender wire and checked ohms and get about 248 on both sides. We removed about 20 gallon from one side and the ohms remained at 248. That reading is at the high end of the scale and the way I understand it means the float is at the empty position.

Either both floats have come off or they are stuck in the down position. What are the chances of that happening to both units?

I'm not that familiar with the RV-10 tank but I assume they are installed the same way as my 9. Any trade secrets that someone can share would be appreciated as I'm sure removal and rebending float rod will be necessary.

Mine read 240-241 ohms empty. Yep, sounds like you will need to pull them out. Use proseal instead of cork gasket going back together.

We had a very similar problem with our RV-3 a couple of months ago (only on one side). The bottom line is that yes, the senders will have to come out, but this thread might give you an idea what MIGHT be wrong.... (and some folks ideas on how to stop it from happening again).

http://www.vansairforce.com/community/showthread.php?t=83306

Wow, I'm glad this topic came up. We'll be hooking up the wires to the senders soon and I'm glad I found this topic the easy way! Thanks for the heads up.

Wayne Gillispie said:

Let me guess...QB wings. Mine read 240-241 ohms empty. Yep, sounds like you will need to pull them out. Use proseal instead of cork gasket going back together.

Click to expand...

I would avoid the stock PR1422/CS3204 B-2 Proseal with a passion. It will make later removal of the sending units near impossible. Either neoprene gasket, or the non-hardening version of Proseal..PR-1403 or equivalent are superior solutions to allow future maintenance.
The only item that is likely to cause a float to hang up is your vent tube. That should have been checked when installing the sending units(which don't come with QB Wings). I know one of my vent tubes required some bending to obtain clearance for the float. However that would cause a full indication, not empty.

Follow up

The problem was found today when the sender unit was removed.

The sender rod was not given the 90 degree bend with 3/4" tail in the rod that goes through the pivot hole in the sender and prevents rotation of the float and rod. It originally worked long enough to calibrate but eventually rotated and rested in the down position.

The plans show the 90 degree bend in the middle of the rod clearly but it is easy to miss the second bend at the sender end.

I forgot to take pictures to that would make a lot more sense than my rambling, sorry bout that.

Yep. Spent hours trying to figure out why the float wouldn't stay put. Luckily worked it out before closing up. The plan is not very clear.

Oh yes - that little bend on the end.....I remember learning about it as I closed up my RV-8 tanks year's ago - I kept wondering "what is going to keep that thing from twisting?!"

The plans are somewhat "obscure" on this point. I pointed this piece of trivia out to Louise when she bent the floats on the RV-3 project.

Paul