Strange Fuel Quantity Indication

We are having difficulty calibrating the fuel tanks on our RV-10. The sensors are resistance type float sensors and the interface is a Chelton EAU. Our problem is the fuel quantity for each tank varies as a function of engine RPM (about a 50% reduction as RPM is increased from 1000 to 2000). Anybody seen anything like this?

Barry

By any chance are you using strange fuel?

Sorry, couldn't resist.

Have you actually measured the voltage coming from the senders while the engine is running to rule out that the actual output is correct / incorrect? You need to start there.

Then you would need to insure that your EFIS is configured for the correct sensor type (there's more than one type of fuel sender) and that the outputs are hooked up to the correct pins on the EFIS (I once heard someone made one or two mistakes in wiring, can't remember who...).

If everything else is ruled out then you need to contact your EFIS manufacturer.

Bill:

Boy, I wish it was as simple as "strange fuel."

I was monitoring tank output with an oscilloscope. It was strange....a DC level with a string of square wave data appearing periodically (square wave amplitude was about 10% of the DC level). I wasn't able to sync the scope to the square wave data but it appeared to appear more frequently with increase RPM. I suspect that I'm somehow getting a summation of the two signals. It dissappears when the engine is cut off.

I'm going to take another look with the scope to see if I can sync up on the serial data string (at least I'll then be able to determine if it is appearing more frequently as a function of RPM).

I'll also go through some checks to see if killing the Alternator field, fuel pump, and anything else I can think of has any effect on this data stream.

I'll keep you up to date on what I find.

Thanks for following up.

Barry