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Multiple fuel flow transducer failures.

JackinMichigan

Well Known Member
I have the EI FT60 'Red Cube' flow transducer mounted in the center tunnel up near the firewall, just forward of the electric boost pump. It's the most inaccessible component on that entire airplane, and I neglected to install an access panel when I had the chance.

It failed after only 20 hours. I spent nearly 3 weeks taking everything apart to get at it and replace it, and the new one functioned just fine after several tests. That is, until I got the entire airplane put back together and had it out on the tarmac for engine startup. That's when the new transducer failed, with essentially zero hours on it. I had to walk away before I took a crowbar to that **** airplane.

This transducer is not in a high heat area (125 degrees F has been the max tunnel temp so far) and vibrations aren't excessive. Does anyone know what would cause these things to fail so quickly? I consider the flow sensor as a mission critical piece of equipment - the plane won't fly if it's not working.

P.S. - Do yourself a huge favor and install an access panel in the tunnel everywhere you have a critical piece of equipment. You will thank yourself later.
 
Reading off scale low, or high, or leaking? Do you have fuel flow?
The internal orifice is kinda small---see Dan Horton's autopsy of one. VAF thread on the subject. Generally electrical if it doesnt read.
Tom
 
Wouldn’t it be better and safer to put the fuel flow sender FWF downstream of the fuel pumps? On injected motors, many are putting the fuel flow sender downstream of the servo and prior to the spider. I moved mine to this position (RV7A) and solved three problems and now it works good.

Bevan
 
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What was the failure mode of the first one? e.g., impeller stuck/won?t spin? Internal electrical connection?
 
Reading off scale low, or high, or leaking? Do you have fuel flow?
The internal orifice is kinda small---see Dan Horton's autopsy of one. VAF thread on the subject. Generally electrical if it doesnt read.
Tom

Reading zero. Not leaking. I have it hooked up to a Garmin G3X for readout.

I had a local A&P share with me a trick to determine if wiring is the issue. Take a piece of wire and, with the transducer fully hooked up, splice it into the signal wire. Tap the other end of that wire to ground. This will simulate a signal coming from the transducer, and if everything else works you should get a reading. That's what I did and was able to get a reading, indicating that it was the transducer itself that failed. After I got it off I notice that the impeller wasn't stuck or clogged, it just quit working.
 
I'd try to get a second or third set of eyes on this. You may be just the victim of incredibly bad luck, or there may be something obvious that you as the builder are overlooking from habit.
Wires oriented up? input attached to "IN"? What sort of thread sealant did you use? Did you blow compressed air thru it to make sure it worked (don't!)? Exceed the recommended torque on the connections? Possible intermittent electrical connections (the worst to trouble shoot)? Any foreign objects in the fuel line?etc....
Call the manufacturer and ask for help. If they've had two in a row fail like this they should be interested.
 
Fuel flow transducer

My guess is the transducers are not the problem, but an intermittent wiring connection is. What is the probability that you could see that many failures when the rest of us almost never see failures where the wheel is not stuck? Memory is the wheel spins in front of a light and a photo cell sees flashes as the wheel obstructs the light when it turns. The photo cell is a modulated output dependent on how fast the wheel turns, this measures flow. The wheel can get stuck, the light can burn out or the photo cell can fail. Or? any of the 3 wires can have an intermittant connection.
 
I'd try to get a second or third set of eyes on this. You may be just the victim of incredibly bad luck, or there may be something obvious that you as the builder are overlooking from habit.
Wires oriented up? input attached to "IN"? What sort of thread sealant did you use? Did you blow compressed air thru it to make sure it worked (don't!)? Exceed the recommended torque on the connections? Possible intermittent electrical connections (the worst to trouble shoot)? Any foreign objects in the fuel line?etc....
Call the manufacturer and ask for help. If they've had two in a row fail like this they should be interested.

+1

With the second unit failing just as quickly, I would be looking beyond mfg defect.

One thing to look at is voltage. The red cube runs off 5 volts, not 12. Most EIS systems provide a FF power pin, but some expect you to tie into the instrument's general 5 volt bus.

Larry
 
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Possible, but highly unlikely, that you've killed two of these units. I would strongly suspect a wiring issue.
 
One thing to look at is voltage. The red cube runs off 5 volts, not 12. Most EIS systems provide a FF power pin, but some expect you to tie into the instrument's general 5 volt bus.

Larry

I think for some time now they accept 5 - 30 volts.
 
Ground Check

Do a good ground connection check between the instrument chassis, Engine and fuselage. It could be some stray currents during the engine start, typically due to grounding issues.
 
I have mine mounted under the front of the engine between the Bendix and the spider. I secured it to the case on a short piece of bent spring steel to give a little vibration absorption and in a position where the output is canted upwards a bit per OEM recommendation. It?s been dead on accurate and trouble free for over 500 hours.
 
I have mine mounted under the front of the engine between the Bendix and the spider. I secured it to the case on a short piece of bent spring steel to give a little vibration absorption and in a position where the output is canted upwards a bit per OEM recommendation. It?s been dead on accurate and trouble free for over 500 hours.

Myron, Do you have a picture of your install? Lynn
 
The second one failed before the first engine start.

Highly unlikely that a brand new transducer failed before first engine start. No one blew air through it did they? I had mine mounted in my -10 in the tunnel after the electric fuel pump also. It was very accurate there in the -10. I wrapped it in fire sleeve for a little heat protection just because I had some on hand. I would start troubleshooting the wiring. Ping it out, verify and triple verify the pin-outs. Check if a pin got folded over. Check the wiring shield braid for a stray strand, or even a pin that has a stray wire strand poking out. A stray wire strand can cause intermittent issues. My buddy had one in his magneto that only acted up when the mag got hot on his G3i set-up. We spent a lot of time trouble shooting that one!
 
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