Fuel flow fluctuations, xTremeEMS, Floscan

Hey everyone

I'm having an issue with my fuel flow indications. I originally installed a Floscan fuel flow sensor along with an RMI uMonitor in my IO-360-A3B6D powered RV-8 12 years ago. A couple of years ago, I upgraded to the MGL xTremeEMS and just kept the fuel flow sensor. It worked just fine up until a week or so ago.

At that time, I replaced my panel because I moved some stuff around. Since then my fuel flow is random...ish. It shows 0 L/hr (I have it set to liters) at idle, then sometimes between 7 (about 2 g/h) and 15 ish (about 4 g/h) at run up. I get in the air and it varies between 20 (about 5 g/h) and 105 (!! about 28 g/h - not possible with an IO-360).

I thought it might be a bad ground, but have confirmed those are good. The fuel flow requires a 5.6K resistor on the RDAC unit and that checks out fine. The confusing part is that all sensors go into the RDAC unit on the firewall, and then the data is sent via RS-232 to the display. All other indications are good, so I'm left with the conclusion that the fuel flow sensor itself has failed. Could one of the failure modes be varying flow indications? It isn't like the numbers jump randomly; they smoothly go up and down, and sometimes just go to zero and stay there.

Any insights would be appreciated.

The Xtreme EMS installation manual suggests using the RDAC 5V source for the pull-up. I initially used this method for my installation.

Eventually I saw fuel flow "wander" from less than 1gph to more than 18gph.

Matt at MGL questioned if my pull-up resistor was going bad. I tested it and it was fine. I replaced it anyway with a 2% tolerance resistor. This did not resolve the issue.

I stumbled on an old installation manual for an older RDAC which did not have the 5v source. It said to use a 12v source. I spoke to Matt about it and he said the RDAC could use any source from 5v-14v.

I switched my pull-up source to use the 12v that was powering the RDAC. Since that change, my fuel flow has been stable.

I suggest talking with Matt or another MGL representative to decide if the same change will work for you.

Thanks for that, Glenn. The description of your problem closely mirrors my own.

I'll drop MGL an email and see what they say.