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Fuel flow (red cube sensor) reads 0 during flight. Any ideas?

ao.frog

Well Known Member
Hi folks.

During a flight yesterday, I noticed that FF indication on the AFS 4500 intermittenly where reading 0. Since it was not dashes but 0, I assume that it was the red cube who where sending a false signal to the 4500.
The engine was running normal the whole time, with normal EGT and CHT indications.

Reason for the assumption is that I think I remember from the install, that when the 4500 does not receive any signal, the corresponding line reads dashes.

During the rest of the flight (15 mins in a straight line back to my home field), the FF intermittenly showed normal indications, but mostly 0. Never any dashes.

This weekend I'll check all connections and lines to see if I can find anything wrong. If not, I guess a new red cube is the only way to go.

The engine, a stock Lyc IO-360, the the 4500 and the red cube was installed in 2012, first flight 2014, and TT is now 240 hrs.

Has anyone experienced a red cube indication failure after 240 hrs? Or is it something else going on here?
 
I have had similar indications on my 0-360. I have a carb setup. If I do not lean the engine, the readings are what I would expect. When I run at 2400 rpm, and lean the engine out...that is when I can see 0 gph and then it goes up to 4 or 5 gph and then back to zero. Repeat / repeat/...

I tried to noodle this out and the best I could come up with is: the carburetor floats are moving up and down in the float bowl. When the bowl is full there is zero fuel flow. As the bowl empties and the floats lower, then fuel flows and the red cube indicates fuel flow. That is my best guess.
 
Sounds like you both need to check the connectors but most likely replacement of the red cube is the fix. BTW, when mine did this it took a new unit to fix and I found AFS or Dynon the least expensive vendor. Another BTW, a few friends have had the same similar issue and a replacement of the red cube was required.
 
New Cube

My first lasted 150 hours. Its located beneath the baffles hanging down from the spider after the servo. I put a cooling blast tube on the new one, thinking heat may be its downfall. I Just replaced my second one after 250 hours. It was 13 months old so past the 12 month warranty. Not sure if they?d cover it anyway. I consider it a recurring maintenance item for now. Less than a dollar per hour. Flying too much to think about changing its mounting location.
 
I've been wrestling with strange ff readings with my IO 320 utilizing the Red Cube. I've replaced wiring, sent it to EI who swears it checked out with both water and fuel, had my injection system checked out by AFP and replaced the hoses. Still gives wonky readings at times. Had Savvy double check my data, too! I may look for a different totalizer since I didn't have this trouble with the FloScan. Hmmmm.........
 
I've been fighting with Red Cube intermittent readings for many years. I've checked and / or replaced everything I could think of, including 3 Red Cubes. I've now moved my factory tested Red Cube from the servo to spider location to the gascolator to boost pump location. The techs at EI claim the readings will be accurate at this location. So.. I'll see on my next flight.
 
My first lasted 150 hours. Its located beneath the baffles hanging down from the spider after the servo. I put a cooling blast tube on the new one, thinking heat may be its downfall. I Just replaced my second one after 250 hours. It was 13 months old so past the 12 month warranty. Not sure if they?d cover it anyway. I consider it a recurring maintenance item for now. Less than a dollar per hour. Flying too much to think about changing its mounting location.

It would've been covered under warranty. Never a bad thing to ask. :) Matter of fact, if you provide me with the serial number, I will be happy to look it up. If it does fall under our warranty, send it in to us. If we verify that it has failed, I will send you a replacement at no cost.
 
RED CUPE READINGS

Well I guess that I'm now part of the erratic Red Cube Readings club...:)

I had the same symtoms over the last couples of months but was too busy flying to have a look at it..

Well 2 days ago, I finally got to work on it and replaced my 5-6 years old Red Cube with a new one...

Initial run up reading appears to be spot on but I will fly the aircraft tomorrow and will check the readings...Fingers crossed..

I also wrapped mine in Fire Sleeve just to shield it a little better eventough I don't think heat was the issue here..

Bruno
[email protected]
 
Thanks for the replies folks. Ok, so it seems like it'll be a replacement then. NOT impressing regarding the service-life of the red cube though... oh well, I'll contact Rob and his exellent crew tomorrow and buy a new red cube from them.

Too bad that it'll take at least two weeks to get it over here, and of those two, at least one week will be in the Norwegian customs and domestic postage.

I'll report back after the replacement and testflight.

BTW: it's mounted on the FF, just after the fuelpump, so it's not exposed to vibrations and heat. From there. the fuelhose goes to the injector.


Before the failure, it has shown VERY stable and accurate FF indications.
Thus, the total fuel in the tanks shown on the AFS-4500 has been within 2-5 litres of the actual remaining fuel amount every time I have fully filled up the tanks.

So up until now, I've been VERY impressed both by the 4500 and the red cube.
 
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We replace quite a few of these that fail in 100-200 hours when they are not heat wrapped in the engine compartment.

Vic
 
We replace quite a few of these that fail in 100-200 hours when they are not heat wrapped in the engine compartment.

Vic

EI FT-60 rated 125 deg C. Under $200. Been manufactured for how long? Made by EI or ?

FS 201 rated 100 deg. C. Over $300.
Been around forever and made by FloScan, specializes in fuel flow applications for many different industries and fuel types.

I have no quantifiable data but it sure seems like there are a lot more failures of the EI units and nobody seems to know why. I can only assume some manufacturers started using them for cost reasons.

I have my Floscan mounted in the upper plenum. My testing concluded that in that location you should never see anything above 100 deg. C., hot day, hot engine, long taxi and monitored for several minutes after shut down.

I have no answers, just my observations.
 
I agree that we don't see failure when they are on top of the engine, but we heat wrap them anytime we see them unwrapped, no matter hwere they are.

Many times I see the red cube mounted with the inlets and outlets in a vertical position, especially when mounted between the fuel air servo and the spider. That may be contirbuting to the gymbal wear as well, as they are supposed to be mounted horizontally with the wires coming out the top. That keeps the vane in a vertical position.

Vic
 
I agree that we don't see failure when they are on top of the engine, but we heat wrap them anytime we see them unwrapped, no matter hwere they are.

Vic


I used to have my FS201 wrapped as well, per JPI installation instructions. However, when I upgraded my hoses, at the recommendation of the hose supplier, I did not wrap it.
If you choose to heat wrap it, how do you inspect the fittings for leaks without taking off the wrap?
I can see my fittings through the oil door and inspect them literally every flight. I can see all other fuel fittings through the exhaust tunnel. ( I don?t take a flashlight and crawl under there every flight but do so occasionally,)
I am uncomfortable just checking at CI.

I am sure a gross fuel leak would show up but firesleeve will hide weeps.
It?s a trade off. Not sure there is a right or wrong answer but I want to see if a fuel fitting is starting to weep as the next symptom may not be a weep.
 
You only need to wrap the cube. You cuould still leave the fittings exposed to see them for inspection.

Vic
 
Timely...

This is a timely discussion for me.

1) Just over a week ago I flew in someone's RV-10 and theirs has the issue where the fuel flow reading is all over the place, often dropping to zero, during flight. The plane has approximately 400 hours, I believe and I think it's been happening a while.

That led me to exclaim "me too" when flying in that plane, because:

2) My RV-14 has the red cube, and somewhere after 200 hours I started having the same thing happen. I'd say that 90% of the time or more, it works fine, but, it's not uncommon that it starts to drop in fuel flow, and sometimes hangs out at zero for a couple minutes at a time. It's mounted in the standard RV-14 location, and, from day 1 I had aluminium tape and fiber insulation around it. When it started acting up, I removed the cube, inspected the wiring, and re-installed, this time with fire-sleeve material over it, and then wrapped in aluminium tape which generally has always kept things cool for me in other applications. Still, at over 350 hours, it's a continuing thing that plagues me. I did purchase another red cube and am waiting for a good time to install it.


Contrast that with my floscan in my RV-10, and that sensor has been working non-stop for over 1400 hours. It seems that I see an awful lot of red cube issues on VAF, which is strange because generally I get the feeling people feel it's the superior sensor. I know it LOOKS better than the floscan, but the statistics seem to be against it. I'm not interested in buying a 3rd, so if this second one fails, I'll go a different route.

I did bring it up with EI at OSH, and was basically told that they're super reliable, seldom fail, and it's probably a wiring issue on my part. It's not rocket science to wire, and since it works 90% of the time, it's probably not that anyway.

I did also speak with another RV-10 person last week who said they have had the same problem with theirs.
 
I've got 395 hours on mine so far. I mounted it on the cool side of the firewall, and while it reads high with the boost pump on, it's dead-on accurate in cruise flight. If I ever forget to turn the boost pump off, the high reading is a good reminder to do it!
 
That's the way I feel about the one in the RV-10. It reads high if you leave the boost on, but otherwise it's fine. And, if you're going to have an error, you want it to be where it reads high so you assume you have less fuel than you really do...not where it reads low or zero so you actually don't have as much fuel as what it says you do.
 
My FloScan is also mounted on the cool side of the firewall and it also reads all over the place on my O-360, carbureted RV4. Occasionally it seems accurate, but as far as being a useful gage of fuel remaining, it’s pretty much useless. The Vans float gages aren’t much help. They indicate full with only 7 gallons on board, and a smiggen below half, you are empty. My ‘fuel gage’ is my watch.
 
Good news!! Great Service.

Sent DAVE Arata (post #7) my serial # and he advised that it was covered by their warranty. Gotta love VAF and suppliers like EI that stand behind their products.
I plan to wrap my currently Installed cube in fire sleeve to see if that gets me more hours of service.
As for checking the fittings, I do this every time I remove the cowl. At a minimum at every oil change, which for me is every 2 to 3 months.
 
What is their warranty? Mine came with my GRT system in late 2015. But not sure if I should bother contacting them. How old was yours?
 
What do I wrap the cube with? Getting ready to put one in (builder had one but removed after it failed, wiring is still present and he gave me the fuel line).
 
You can use other heat suppression fabrics and things if you wish, but this is one option sold at Spruce:
FUEL TRANSDUCER COVER FIRESLEEVE BLACK 1-1/2 ID
Part# 05-07119

https://www.aircraftspruce.com/catalog/appages/gbfireslvft.php?clickkey=5892

I would also recommend covering it further with something silver reflective.

Also, on any exhaust near by, use heat shields like these:
EXHAUST SHIELD ES-2 2 INCH
Part# 08-07351
https://www.aircraftspruce.com/catalog/eppages/exhaust_shield_2_2.php?clickkey=7730

Also available in longer lengths.
 
It will not be near exhaust, based on where the wires are at it is going to be close to upper left side of the firewall. Thanks for the help.
 
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