Posted for "glong2" <glong2@netzero.net>:

 Dan:
 I have had a similar problem but my fuel gauge read near zero when I knew
 there was 30 gallons in the tank. After troubleshooting for about a month I
 found that my capacitance probe had collected water in the cap at the lower
 end. I removed the probe as far as I could without taking the wing off and
 dried it out, the probe worked fine. I then added a small amount of water to
 the probe and the squirrelly behavior reoccurred (I used external
 capacitance to simulate fuel).
 
 The probes have two holes in the outer jacket at the nut end of the probe.
 It turns out my probe was installed so the holes were horizontal and water
 could collect in the probe. When I reinstalled the probe I made sure the
 holes were vertical so no water could collect and I have had no trouble
 since. I believe I got the water because I let the right tank set near empty
 for two weeks.  After the tank set nearly empty, I also had a drop or two of
 water when I drained the sump. for about two weeks. I now keep my tanks
 nearly full and have had no sump water indication since.
 
 I replaced the fuel selector valve because mine was leaking and would not
 shut off in any position. The left tank leaked when  right was selected,
 right leaked when left selected, and both leaked when "off"  was selected. I
 found this when I was calibrating the gas tanks and had one empty. I talked
 to Vern because I was concerned if I ever run one tank dry then the gas in
 the other tank may not be available because the fuel pump would suck air
 from the empty tank - a disaster waiting to happen!  Vern sent me free of
 charge the Andair valve and I replaced the older one.
 Eugene Long
 Lancair Super ES
 glong2@netzero.net