Red Cube Problems
 

My plane has flown great the past year and I am starting my 1st condition inspection. One of the few squawks I've had is my fuel flow has been fluctuating the last couple of months. One minute it is reading 8.2 gph and the next minute it will go to 9-10 gph. I recently completed a trip where the fuel flow was reading like this sometimes as high as 10 gph for a 3.5 hr stretch in LOP cruise and then go back down to 8.2gph without changing any cruise settings. I stopped to fill up and my fuel burn was 8 gph average and the totalizer was 4 gallons more than actual. The first 80 hours on plane the fuel flow and totalizer was perfect every fill up. Has anyone else had these problems and is replacing the red cube my only cure? The pic below is how I have it mounted.

Was your fuel pressure fluctuating also, by chance?

Just some thoughts.
 

Mike, it seems to be either reading high, or a poor connection wiring connection/inteference. Since the cube is in the sub-atmospheric pressure region and might collect some air bubbles there, you might look for some tiny suction leak that has developed. Testing between the wing root and cube is a good section to diagnose. Purge that line, block the fuel at the cube, and pressurize with air at the root with a gage and shut off valve. If the pressure does not drop in a couple of hours, then consider relocating the cube between the servo and spider, or contacting EI about cube replacement.

Only looking at some data from the signal can determine if a bad ground or other poor connection exists on the electrical side.

Pressure steady as a rock.

Mike
I had the same issue recently and went thru many of the same things that could be wrong or causing the problem. After 3 weeks of little changes checking connections, conversations with EI I replaced the Red cube and my problems went away. I have 650 hrs on my RV-10 and this is the 3rd red cube. The first one just quit working one day and the second one was doing what yours was doing. It started out fluctuating about .3-.5 then was up to 1.2 to 1.3. I would go from LOP to ROP.

I have checked all my wiring and voltages and the only cure was a new one. I think the EI fuel transducers quality is hit or miss.

FWIW

Geoff

That's what I was afraid of! :mad: Well, the good news is I can dissect the old one and see how these things work!

Mike---this ties in with the thread posted by Randy Crothers (kind of) about fuel pressure fluxuation.
Please keep us informed on the outcome of your checks.
Tom

Just a data point concerning failure of the red cube. In my build I was concerned about heat causing issues with the longevity of these cubes. Consequently I placed both of my cubes (have two, one is for the return fuel line) on the cold side of the firewall. 6 years (knock on wood) and no sign of problems.

Mine has been on the cold side of the house for 4-5 years now and so far so good. The accuracy of this side of the house is within .2-.3G for every fill up (25-30G) and that is good enough for me.

When I had issues with fluctuating fuel flows, EI told me that the #1 cause was poor electrical connections. Despite having crimped on knife splices, I took them apart and simply soldered the wires together and covered with heat shrink. They have been rock solid and accurate ever since.