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Red Cube issues...

MacCool

Well Known Member
I have an FT-60, firewall mounted, on my RV-9A with IO-320...TT380 hours...and it reads on the display of my AFS 5400 EFIS. Over the last few days, I'm getting intermittent fuel flow readings, sometime low, but more usually it either reads zero fuel flow or it reads what I take to be normal. It will go on and off several times in a flight. Every time it goes offline, I get a "check fuel computer" audio warning.

I realize that the first thought is going to be "dead Red Cube" as this seems to be a recurring theme with that device and the symptoms are pretty classic. I'd just empirically replace it, but for a little backstory:

I recently replaced my legacy AFS 4500 with an AFS 5400. In the wiring switchover, the Red Cube didn't make the trip and I ultimately found an install manual error on the wiring leading to the FT-60 not getting any power from the EFIS. I noticed this by putting a voltmeter on it, reading zero volts all the time. Not intermittent like it is now. Once I got the harness re-pinned, about 3 weeks ago, it's been working fine. I did re-check the harness today and the Red Cube is getting the normal 8 volts, at least at that moment, with the plane sitting on the ground. The connections all look solid and pass the jiggle test.

Question...is there some other way I can evaluate the FT-60...bad power connection vs bad wiring other than just installing a new one?
 
Try cleaning unit.

There’s a very small plastic turbine wheel that spins inside that sends the pulses.
There is a possibility it’s hung up from some contaminate. It doesn’t take much to stop it since it’s made to bypass fuel in the event that it does bind up. Try removing it and spraying carb cleaner back through it paying special attention to any debris that may fall out. It’s worth a try before buying new.
 
Mine started giving the same symptoms a week or two ago. I pulled it and ran a bunch of carb cleaner through it and unfortunately no improvement, so that approach unfortunately is not universally successful, though certainly worth the effort to try. It seemed clear that the paddle wheel was spinning freely (a light blow through the unit would keep the whell spinning for at least 10 seconds) in the chamber, so suspect it is an issue with the electronics buried within or the optical sensor/light source failing. The red cube uses an optical sensor to report each passing vane on the wheel as it spins. I speculated that the plastic lens on the LED or sensor clouds over with long term exposure to fuel and at some point degrades the light enough that the sensor starts to miss the on/off light signals.

Larry
 
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Mine started giving the same symptoms a week or two ago. I pulled it and ran a bunch of carb cleaner through it and unfortunately no improvement, so that approach unfortunately is not universally successful, though certainly worth the effort to try. It seemed clear that the paddle wheel was spinning freely (a light blow through the unit would keep the whell spinning for at least 10 seconds) in the chamber, so suspect it is an issue with the electronics buried within or the optical sensor/light source failing. The red cube uses an optical sensor to report each passing vane on the wheel as it spins. I speculated that the plastic lens on the LED or sensor clouds over with long term exposure to fuel and at some point degrades the light enough that the sensor starts to miss the on/off light signals.

Larry

Great explanation. My FT-60 is on the firewall immediately adjacent to the electric boost pump which is also mounted there. I'm sure it's not an optimal environment for a mechanical/electro-optical device. The FT-60 does appear to have some longevity issues. Fortunately, not terribly expensive at 0.2 AMU.
 
Great explanation. My FT-60 is on the firewall immediately adjacent to the electric boost pump which is also mounted there. I'm sure it's not an optimal environment for a mechanical/electro-optical device. The FT-60 does appear to have some longevity issues. Fortunately, not terribly expensive at 0.2 AMU.

agreed. $200 is a small price to pay for using fuel flow data to best manage the engine.
 
The Red-Cube should be getting 12-14v. Maybe the 8 you measured is the issue?
 
The Red-Cube should be getting 12-14v. Maybe the 8 you measured is the issue?

We went through that with Rob extensively and were assured that the FT-60 would work just fine on the 8 volts that the 5000-series EFIS provides. EI confirmed.
 
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Practiced what I preached

Having had my FT-60 fail just last week I pulled it today and cleaned it out.
Didn’t find any debris and was able to lightly blow into the IN port to hear the turbine wheel spinning nicely. Wiring was checked and all grounds and voltages checked out. :) I reinstalled and pulled her out to test.
No Joy. :eek: Order is in and should have the new unit in a couple of days. :D Vic Syracuse told me when he inspected my plane that he liked the mount on the FW but suggested some insulation and shielding to keep it as cool as possible. My unit only had about 50 hours flight time but was actually about 15 years old. Probably electronic degradation. Same thing happened with my brand new 10 year old com. Sent it to ICOM and electronic degradation was the magic word for that too. Only advice I have now is to wait till you actually need it before you buy anything electronic. ;)
 
Having had my FT-60 fail just last week I pulled it today and cleaned it out.
Didn’t find any debris and was able to lightly blow into the IN port to hear the turbine wheel spinning nicely. Wiring was checked and all grounds and voltages checked out. :) I reinstalled and pulled her out to test.
No Joy. :eek: Order is in and should have the new unit in a couple of days. :D Vic Syracuse told me when he inspected my plane that he liked the mount on the FW but suggested some insulation and shielding to keep it as cool as possible. My unit only had about 50 hours flight time but was actually about 15 years old. Probably electronic degradation. Same thing happened with my brand new 10 year old com. Sent it to ICOM and electronic degradation was the magic word for that too. Only advice I have now is to wait till you actually need it before you buy anything electronic. ;)

it must have been all the lead in the avgas that coated the sensor window. That lead is a real problem, I heard Osh needs to rent a tractor to clean the field after AirVenture.
 
it must have been all the lead in the avgas that coated the sensor window. That lead is a real problem, I heard Osh needs to rent a tractor to clean the field after AirVenture.

Absolutely agree! If 93 octane, ethanol-free, lead-free, Lycoming approved "mogas" was readily available, I think that most of us would switch in a heartbeat.
 
Method to clean out lead.

it must have been all the lead in the avgas that coated the sensor window. That lead is a real problem, I heard Osh needs to rent a tractor to clean the field after AirVenture.

Interesting. I’ve read posts by others that said dismantling the cube is almost impossible since something usually breaks in the process. I would love to test out your theory by cleaning out the lead. Does anyone know of a chemical liquid I could fill the cube with that would flush out the lead.
It’s worth a try.
 
Interesting. I’ve read posts by others that said dismantling the cube is almost impossible since something usually breaks in the process. I would love to test out your theory by cleaning out the lead. Does anyone know of a chemical liquid I could fill the cube with that would flush out the lead.
It’s worth a try.

Such products exist for firearms, but I have no idea how well they work even in that context, let alone whether or not they'd be suitable for use in an electronic flow sensor. I guess the value of trying such a thing depends on how bad you want to save the $200.

https://sharpshootr.com/no-lead/




...
 
Hoppes no. 9 is the traditional gun barrel cleaner for lead, copper, powder fouling etc. but the side effects on a FT-60 would be uncertain.
 
Hoppes no. 9 is the traditional gun barrel cleaner for lead, copper, powder fouling etc. but the side effects on a FT-60 would be uncertain.

Hoppes No. 9 works as well as anything for powder residue, and the smell is the most traditional thing about it :), but it’s not great at all for dissolving lead IME.
 
My experience was that the lead turns into a grey goop after filling the spark plug electrode cavity with Hoppes #9 and letting it work overnight. You can clean the spark plug but I don't want it in my Red Cube.
 
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Raise my hand

it must have been all the lead in the avgas that coated the sensor window. That lead is a real problem, I heard Osh needs to rent a tractor to clean the field after AirVenture.

Sorry I should have raised my hand.
It was a joke, based on another thread that had gone off the rails.
 
Getting back to this thread FWIW, I did replace the Red Cube at my last condition inspection and it solved the the fuel flow problem. I recalculated the K-factor and the fuel computer in my Advanced Flight EFIS is now accurate to 0.1 gallon.
 
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