Capacitive Fuel Senders/Gauge

[ExtraKatana]

About to remove my 8's tanks to dig into a fuel level sending issue that has been bugging me for a year. I have an EI gauge(FL-2)with what I believe are capacitive plates in each tank. I have replaced the IC Modules that are just outside the tanks already. They are inaccurate even after calibration. One flashes I have 0 fuel on ocassion. Actually saw some fuel seeping through the BNC connector on the side that shows more accurately. Have cleaned the connections to the gauge and to the tanks with no resolution. Any hints or good reading out there to research before I start removing tank bolts? Anyone have significant knowledge with the capacitance plate system?

[pilot2512]

Can't help with the t/s but I do have a pair of IE P-300C convertors new in the bag if you have that style converter and need them.

Jay

[ExtraKatana]

Is that a sensor used in lieu of the plates? Pricey buggars.

[FinnFlyer]

Unlikely, but not impossible that the fault is in the tank. Would have to be bad solder connection or loose screw holding plates to ribs. Or perhaps the nut holding the BNC connector to the root rib. The last one critical to ensure proper grounding and reliable capacitance readings.

I think I would try with different converters (or swap left and right converters) before I would even dream of removing and opening the tanks.

Edit: I'm assuming Van's capacitance plates.
Never mind. I now see you already replaced the converters

Finn

[ExtraKatana]

By converter you mean the EI module they call the IC Module. I already bought a new one and soldered it in 6” from the BNC…where the other one was. Reprogrammed the EI FL-2C and everything was great until the 5th minute where I made a steep turn. Went to “0” on a full tank. It is intermittent.

[FinnFlyer]

Originally Posted by ExtraKatana

By converter you mean the EI module they call the IC Module. I already bought a new one and soldered it in 6” from the BNC…where the other one was. Reprogrammed the EI FL-2C and everything was great until the 5th minute where I made a steep turn. Went to “0” on a full tank. It is intermittent.

Then, the only thing I can suggest is check BNC connector and cable for bad solder or crimp before getting into the tank. Try to wiggle BNC connector in the tank. You may be able to inspect the outer plate through the filler opening.
I don't remember if the RV-8 tanks have an access panel in the root rib.

Edit: The fact that it intermittently goes to zero would point to a bad connection at the BNC connector. Could try adding a ground wire from tank to ground of BNC.

Finn

[ExtraKatana]

Good ideas. Thank You. The ground is the exterior of the BNC?

[FinnFlyer]

Originally Posted by ExtraKatana

Good ideas. Thank You. The ground is the exterior of the BNC?

That's correct.

Very poorly shown on the attached PDF drawing, but critical that there is excellent electrical contact between the BNC ground and the root rib (tank). Typically a serrated washer is used that cuts into both the BNC exterior and the rib. At the same time it also needs to be sealed against fuel leak.

Adding a temporary additional ground wire should tell you whether that is the problem area.

Finn

[chaskuss]

Originally Posted by ExtraKatana

Actually saw some fuel seeping through the BNC connector on the side that shows more accurately. Have cleaned the connections to the gauge and to the tanks with no resolution. Any hints or good reading out there to research before I start removing tank bolts? Anyone have significant knowledge with the capacitance plate system?

Your BNC connector leaks because Vans supplies cheapo Made in China units, rather than the quality USA made Amphenol connectors. I have issues with Vans use of hardware store Nylon washer stack & vinyl tubing as insulators. If you want more info on this, send me a PM.

Another issue with capacitance fuel gauges is that ethanol in auto fuel messes up the accuracy.

Charlie

FYI Jim Weir wrote 2 articles in Kitplanes on you to make your own converter modules for capacitance gauge set ups. I have both.

[ExtraKatana]

I wrapped a small hose clamp with a stranded wire around the knurled section of the BNC and attached the other end of the wire to a paint-less tank flange screw where the fairing attaches. The erratic readings stopped, the tank reading on the EI FL2 never went to 0, and fuel was showing to drop throughout my 1 hr. flight. Thank You For Your Help!

So what is still not right on is the EI gauge says I burned 4 Gallons when I burned 8. I need to re-calibrate. A few questions about calibrating these capacitive gauges:
1) Do you get better resolution if you make the 9 calibration points between 0 and 15 Gallons? That's really the zone you want to know what you have.
2) Does the plane need to be level? (Vans plates)
3) Does the voltage need to be closer to an engine-running 14.xV vs. 12V?

Edit: EI has always been good with my silly questions. Here are their answers to the above:
1. Calibrating your points closer together should indeed give you better resolution across the applicable range, theoretically (more accurate up to 15 gallons, inaccurate above this).
2. We recommend jacking the plane up to cruise attitude when calibrating the tanks for best accuracy in similar conditions.
3. I actually don't see any reason why voltage would impact the calibration for a capacitive sender so long as everything is properly powered and operating within tolerances, but once again it is usually best to calibrate with the same circumstances from when you care most about the indication.