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Fuel Flow (GPH) inop or intermittent

J

jimkwalton

Active Member
My fuel flow started being intermittent about 30 hours ago on my -14. Advanced 5600 EFIS and Avidyne 540 navigator. Wires appear to be solid. Fuel sensor (located below left two cylinders) is wrapped with heat protection. It almost always works at start up but either on taxi out or by takeoff I look down and it’s zero. Even those times it’s working, the Avidyne does not seem to pick up the readings.

If any of this makes sense and you know of a cure please let me know.
 
The symptoms seem to point to a failing red cube; They seem to have relatively short lives on occasion. I would first verify there is no wiring issue causing this though.
 
I had the same issue with my red cube/Advanced Flight EFIS at about 400 tach hours. I've read here about people removing it and flushing it out, proposing that something was blocking the little whiz-wheel, or the optical sensor. I opted to just pitch the thing and install a new one, which completely solved the problem. Limited lifespan of those things seems to be mentioned fairly often.
 
A few things to check.

Although the flow orifice is pretty small and unless all the fuel flow passages were pre cleaned and purged before the cube, it is possible it is debris. BUT- - if that were the "cause" the flow would be diminished too. Easy to check and clear, but do not use pressurized air, simply back flow some gasoline or mineral spirits (a small tipped squeeze bottle) over a white towel to see if anything comes out.

Were the fittings sealed with teflon tape? Let's hope not - a trailing piece could foul the wheel and not affect the flow.

Over the years posts electrical issues were not uncommon - I soldered the flying leads/wires (shame shame) to ensure good contact thus avoiding terminal issues.
 
One would think if it is blocked by the debris, it would not work at the start up.
If this behavior is consistent, I would think maybe the heat has some to do with it. I would also not dismiss the possibility of the connection to loosen up by the heat.
 
EFI Advantage

That's one advantage EFI has (EFII & SDS) there is no need for a red cube to monitor fuel flow. It does it by injector timing and seems to be fairly accurate. (EFIS totalizer matches very close to actual tank readings) :)
 
Red Cube

MacCool said:
I had the same issue with my red cube/Advanced Flight EFIS at about 400 tach hours. I've read here about people removing it and flushing it out, proposing that something was blocking the little whiz-wheel, or the optical sensor. I opted to just pitch the thing and install a new one, which completely solved the problem. Limited lifespan of those things seems to be mentioned fairly often.
Click to expand...

Where do I obtain a new RED CUBE?
 
=jimkwalton;1697079]Where do I obtain a new RED CUBE?
Click to expand...

Assuming that your fuel flow sensor is indeed a "red cube" (FT-60 Flow Transducer from Electronics International), most airplane parts suppliers carry them as they appear to pretty much the standard fuel flow transducer for Experimental airplanes. Check Aircraft Spruce, SteinAir, etc. They're $200, IMHO cheap enough that I didn't want to screw around with trying to rehab mine when it started doing what your's is doing.

ETA: My Avidyne IFD440 doesn't get fuel flow from the red cube. Fuel flow goes to my Advanced Flight EFIS and the Avidyne gets the info from that. Note that you'll have to recalibrate (enter a new K-factor into your 5600). It probably won't be too far off from the K-factor you are currently using, but make sure that you know what that is since New K-factor = (computed fuel used / actual fuel used) * your current K-factor.
 
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My experience as well.

jimkwalton said:
My fuel flow started being intermittent about 30 hours ago on my -14. Advanced 5600 EFIS and Avidyne 540 navigator. Wires appear to be solid. Fuel sensor (located below left two cylinders) is wrapped with heat protection. It almost always works at start up but either on taxi out or by takeoff I look down and it’s zero. Even those times it’s working, the Avidyne does not seem to pick up the readings.

If any of this makes sense and you know of a cure please let me know.
Click to expand...

I also have the AFS system, minus the Avidyne and had the same experience with my Red Cube. I relocated mine to the engine mount, to eliminate the engine vibrations. I even bought a new Red Cube. Still intermittent. Also had intermittent CHT and EGT anomalies. I bought a package of EI wire connectors

https://iflyei.com/wp-content/uploads/OLC-2_web.png

I replaced every spade and butt splice on the sensors and Red Cube with these connectors and haven’t had any issues since. I’m a believer in these things.

Bill
 
When my red cube got plugged with debris the flow went to zero in the span of about 5 seconds and never recovered until I cleaned it up.

This was just the measured flow, the actual flow was not affected - I other words ,the red cube failed “open” as it was supposed to …
 
FT-60 $199 at Spruce

Also, Aircraft Specialties/TS FLIGHTLINES sells a kit to relocate the transducer to the top of the motor by the spider. Closer to centerline so less vibration and away from the hot exhaust/cylinder area.
 
I think I've mentioned this before. We are seeing a higher number of failures of the red cube on RV-14s than any other RV. I think it has to do with the location being in the hot air right underneath the cylinder, which is according to the kit plans.
I recommend wrapping them with some heat barrier tape from Spruce, or better yet, relocating it.

Vic
 
To service the Red Cube and check for debris, do you use an Allen wrench and remove the front or what is the procedure? Mine crapped out just before last flight. I’ve checked connections so maybe debris or just dead. Thanks
 
vic syracuse said:
I think I've mentioned this before. We are seeing a higher number of failures of the red cube on RV-14s than any other RV. I think it has to do with the location being in the hot air right underneath the cylinder, which is according to the kit plans.
I recommend wrapping them with some heat barrier tape from Spruce, or better yet, relocating it.

Vic
Click to expand...

What Vic said….

The Van’s location for the flow sender is horrible and it is easy to mount the cube on the engine mount with adel clamps between the mechanical fuel pump and the fuel manager. If done right this location will satisfy the flow sender install instruction requirements.

Carl
 
As another data point (certainly not saying this is the best way to do it), my red cube is mounted on the firewall. The fuel flow arrangement was a decision made by the guy who did the firewall-forward for the original builder of my airplane. I did have to replace my red cube (intermittent fuel flow variation) at about 400 hours. I have since added insulation to the fuel lines and the red cube, as well as exhaust shielding, in order to try to correct some fuel pressure variation when the engine was hot on the ground taxiing. This arrangement has worked fine for me since replacing the red cube (and the fuel pressure transducer).

Again...I am not advocating this firewall location for the FT-60. It was not a decision made by me, but it works so I haven't opted to change the location at this point.




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Replaced Red Cube

Just replaced Red Cube. All is well now. Except my Avidyne 540 is not picking up fuel information. Any suggestions there?
 
If you try and remove the allen screws in the cover, there is an EXCELLENT chance of breaking them. There are no serviceable parts in there, and a fine wire that you'll probably break getting the unit open.
See Dan Horton's autopsy of one several years ago. The failures we;ve seen were at the wiring harness at the transducer body. So some reason, they break there---might be from harness vibration.

Vic is also correct about the RV14 issues----several have relocated the unit with good results, others have firesleeved them and given some strain relief to the harness.

OH---and as an update---WE have made some minor changes to our mounting bracket to better fit a 'newer' version of the 75009 Lycoming flow divider bracket. The originals we build we prototyped using an OE Lycoming bracket. After 5 years in service, several of you reported a misfit in the aft angle of the bracket verses the Lycoming mount. So we purchased one, and YES there is a minor difference in the 2 Lycoming brackets. Same part numbers, but a difference in the upper bend, and that changed the angle. So we made a revision change, and also opened up the inside roof alittle more to accomodate an easier install. WE should have the next production run shortly.

Tom
 
If resonance is the enemy...

...adding some additional weight, changing the attachment area of the mass, etc. might help.

The RV-14 installation instructions have the builder use MS24694-S72 (FKA AN509-10R30) to attach the Red Cube to the clamps.

I believe that you should use AN4-30 (1/4" bolt) instead of the AN509 (3/16" screw), and drill up the holes in the MS21919WCH26 clamps to accommodate the AN4 bolt.

Just a thought -- it seems to have stabilized/resolved the weirdness I was seeing on my -7.
 
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