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Red Cube Problems

MikeyDale

Well Known Member
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.

25t7r09.jpg
 
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.
 
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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
 
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.
 
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.
 
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.

I think I'll give that a try! Thanks Jason.
 
Thanks Jason! While doing my recent condition inspection, I removed the connectors and spliced and soldered the wires and it has apparently solved my problem. :)
 
Thanks Jason! While doing my recent condition inspection, I removed the connectors and spliced and soldered the wires and it has apparently solved my problem. :)

Thanks for closing this out. That does it, I have been looking at those connectors, as I do other FWF stuff, they will get soldered! Another issue avoided.
 
One more Red Cube failure

I started having a problem with intermittent zero fuel flow (good fuel pressure & engine ran fine) after about 140 hrs TT. Sometimes it would show zero fuel flow at engine start then jump up to normal flow after half an hour or so and remain normal thereafter.

I checked all the wiring and connections and didn't find any problems. I removed the unit and blew low pressure compressed air through it and could hear the wheel spinning inside.

Finally I just bit the bullet and bought and installed a new one and the problem disappeared. Everything normal.

Out of curiosity, I disassembled the old unit to see if I could see a problem. It's pretty simple inside and I didn't see anything that looked like it would cause a problem.

Interestingly, the new unit (from AS&S) came with three connectors, one for each wire, that I hadn't seen before. Each was a small sleeve with an allen screw in the middle. It's like a small butt splice except the wires overlap inside the sleeve and the allen screw is tightened to secure the splice. Seems pretty secure.
 
Had the same problem after 300 hrs: gph drops intermittently to zero, fuel pres normal. Replaced the cube and all ok

added a larger stainless steel heat shield from ACS:

https://imgur.com/D494OMN
 
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