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Fuel Flow Transducer Woes


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Just wanted to put this out there.

 

If your fuel flow transducer fails in a CTLS (possibly the same for the other models), get ready to cry a bit. Here's my experience with it:

 

When my transducer failed, I decided not to even screw with it because of it's location. That is, until it started interfering with fuel pressure. *sigh*. I didn't want to mess with it because it's mounted against the forward firewall, with one of the pipe fittings sticking through the firewall itself, and the fiber lock nuts are under the center riser, above and behind the cabin heat divider. Call up dynon to order a new transducer. Dynon doesn't even sell the old transducers anymore? *Sigh*. Bought the new FT-60 from them and it arrived. I expected the layout would change a bit, but the bolt diameters being different? Oh come on.... Well, until I find the goofy bolt sizes this thing needs, I can, in the meantime, get the old one out. Oh god, band clamps everywhere! I don't have a dremel or a cut off wheel on hand... Off to the store! While I was there I needed to get a band clamp tool and band clamps. Nope, they don't sell any. Crap. Well might as well get the cut off wheel at least. So I go to the next 4 hardware stores, everyone is looking at me thinking "what's a band clamp?" Finally, I try an automotive parts store, a place where I rarely ever like to go simply because of taboos and I don't need people thinking I use car parts on planes... Bingo, they have one! Oh wait, while I'm here, I have an idea! Tap and Die set! I can take bolts that are longer than the application calls for, thread, and cut them down to size. Score! So I got back, and lopped off the band clamp on the gascolator, removed the bolts on the transducer... CRAP! I dropped the washers right down into the very front against the firewall. I don't have arms built for this... I'll make a note to remind myself to figure out how to fish those out later. I pull the old transducer out, and I set the FT-60 in to see what I need to do... Yup, I have to fabricate a new mount. Took measurements, and got that done. As for the bolt holes, I can use one of the existing bolt holes at least, but the other will have to be drilled pretty close to the firewall. I can't get a drill in there to make the hole. *SIGH*. Untied the extra service loops in the console, unbolted the pod, and begin to pull it forward when I decide to take a closer look. Well that's great. I have to unbolt the fuel valve. Even better, I also have to undo the cabin heat and carb heat hookups. This is really getting on my nerves... Get all that stuff disassembled, and everything is accessible now. Check to make sure there is no structure, wires, or tubes there, commence drilling, and new hole for the bolt made! Nothing damaged either, and it's a clean hole. At least I got my measurements right and didn't need to redo anything. The fittings for the two fuel flow transducers are the same 1/4 inch NPT threads. That's gooooo OH WAIT. DAMNIT I don't have any thread seal! Got lucky at the store, one last bottle of fuel compatible teflon sealant. Put sealant on the pipe threads per FT-60 instructions, and torque. Didn't need to put a band clamp on the fitting because I didn't remove the old one (no need to). Put in the new mount and my skillfully made bolts on the transducer to make sure it all looks good, feed the tube through the firewall hole, pull it down, and start sliding on the fire sleeve... well crap. I need string so I can pull the hose through the sleeve, since I can't reach too far up the hose without pulling the engine. Got some string, pulled it through, and looks good! Alright... everything lines up, doesn't look like there's any side load on the fittings... so I remounted the pod. I get to work reattaching the hose to the gascolator and band clamp it, and the fire sleeve over it. Inside, I start reattaching fuel lines, and do a quick and dirty flow test to make sure I'm not wasting my time. Fuel flow well exceeds minimum spec, and the dynon EMS reads the fuel flow transducer perfectly! Now how do I fish out those washers? Oh yeah, I remember an old tool that I had from my electrician days! My flexible claw pick up tool! I go blow the dust off of it, apply a little oil, and it works! It grabs the washers on the first try no problem. So I start reassembling everything, and I remember something.

 

Oh crap. After doing all this, I forgot to do one thing. Fill out the MRA form. Well poop. Submitted that earlier today. At least the FT-60 exceeds all the specs of the old transducer according to all of the tech specs sheets I looked up to provide in the MRA. Wait a minute... what's this link? AIRCRAFT SPRUCE SELLS THE OLD TRANSDUCER? FFFFFFFFFF..... At least the flow rate test is a pass and all specs exceed the old transducer. I go ahead and button up the plane, but I need to wait for that LOA approval.

 

Now watch as I get a denial letter for the LOA for the FT-60.

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Thanks for sharing your experience. I always feel like I'm looking into a crystal ball at my future since our planes are only one serial number (and N number) apart. I'm curious to know what symptoms you saw to convince yourself the unit was bad. My flow display does some strange things once in a while, but settles down and seems to be correct. Interesting to read FlowScan specs showing bearing life 10,000 hours and fail safe blocked rotor hardly affecting flow thru it.

 

http://www.floscan.com/html/blue/aviation.php

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2,200 hours on mine. Basically, when the drop was reported, the CFI noticed the flow rate would spike for a short time. The random spikes happen to 6FD too, so that's why we don't flip out on the first instance, but this happened multiple times that day, during takeoff, and I grounded the plane right then. Oil pressure is zero tolerance, and fuel I don't mess around with (although I do not have an issue with fuel pressure or fuel flow spikes as long as the other still shows normal).

 

After I removed the transducer, I blew into it to see if it was clogged. It was surprisingly difficult to get the impeller spinning on top of the fact that there was a good bit of resistance to my airflow effort.

 

I'm doing other tests too while I wait for the approval, and getting the plane cleaned up some. By the way, meguiar's detailing clay works REALLY well getting the skin back to a really smooth feel. Follow it up with a good waxing, and you won't be able to pull the plane by the tail, it will slip right out of your hands.

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I personally did not see it. I'm relying on the words of a pilot (razzing!). I was told that fuel pressure alarms went off, and the fuel flow transducer was picking up. It was only happening on takeoff, but there didn't seem to be a problem in cruise, pressure would climb back up, and the flow transducer was dropping off.

 

I like the red cube's design anyways. It's straight through, large orifices, and the impeller only sticking up about 1/3rd.

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I had an airplane do something like this after installing the new style fuel pump. I was relating the issues to that. On take off I would see fuel flow up around 10-12 GPH and pressure dropped off to inder 2 PSI. I installed a new fuel pressure sending unit, and the low pressure warnings went away, but the fuel pressure would still read low. This would happen in the climb right after take off. In level flight pressure would come back up and fuel flow would come back down, but not to where it should be. After a few flights the fuel flow was back down around where it should be. I did verify that the actual fuel usage did not match what the fuel flow was saying. This is on a SW, so it will not be as hard to change as on your LS.

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Huh.  I installed the new pump and the engine is purring along just as good as with the old  - i think.   I do not have the fuel flow gauge so i would not know the pressure in flight. -   Ground tests are normal so i would never know if there was an issue with  the pressure  on climb or in flight. 

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Huh.  I installed the new pump and the engine is purring along just as good as with the old  - i think.   I do not have the fuel flow gauge so i would not know the pressure in flight. -   Ground tests are normal so i would never know if there was an issue with  the pressure  on climb or in flight. 

 

I have a fuel flow sensor and a fuel pressure sensor. The flow sensor would not tell you the pressure :)

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  • 1 year later...

Just wanted to put this out there.

 

If your fuel flow transducer fails in a CTLS (possibly the same for the other models), get ready to cry a bit. Here's my experience with it:

 

When my transducer failed, I decided not to even screw with it because of it's location. That is, until it started interfering with fuel pressure. *sigh*. 

Hi Corey,

 

You say that you decided not to worry about the fuel flow transducer failure until "it start interfering with fuel pressure".  What do you mean by "interfering with fuel pressure"?  

 

The reason for my question is as follows:

 

My fuel flow reading became erratic about 8-10 flights ago.  About 6-8 flights ago, it just read zero the entire time.  More recently,  I got a high fuel pressure warning (see http://ctflier.com/index.php?/topic/3199-fuel-sensors-question/). I had the A&P/IA mechanic on the field install a ground wire from the ground bolt through the firewall (2005 CTSW) to the engine as suggested by Roger Lee in another thread.  The next flight every thing was fine.  Last night, I thought that I saw a fuel pressure warning on startup but it disappeared before I could check it.  A high fuel pressure warning appeared just after arriving at the run-up area.  When I checked the display, the fuel pressure was climbing from 9.7 to 10.0.  Ten is the top of the fuel pressure scale on my Tru-Trak EMS (Yes, I have a MRA).  I advanced the throttle slightly (maybe to 3500 RPM) just briefly.  The fuel pressure immediately fell to about 6 PSI within a few seconds.  To trouble shoot, I did a run up to 3,800 RPM and checked the ignition circuits.  Engine readings were normal and fuel pressure was running around 5 PSI.  I taxied back to the hangar and shut it down.  

 

The new avionics and related sensors were installed in 2012 at Flight Design service center.  The new style fuel pump was installed in the fall of 2013.

 

Beyond having both of the sendors checked, does anyone else have concerns or suggestions...?

 

Thanks in advance...!!!

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It's an old post. As I have found out, it did NOT interfere with fuel pressure, but is in fact a problem with the fuel pumps. Rotax says dropping fuel pressure for a few seconds is fine in their fuel pump service bulletin.

 

Now in your case: that's really high, but make sure it's not a sender malfunction first.

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Wow, that was a fast response...amazing timing.  And of course, thanks!  

 

However, in my case, it was a SPIKE in fuel pressure and not a drop.  Unfortunately, I don't know enough about what might cause a fuel pressure spike to feel certain that my trouble shooting would "cover all of the bases" so to speak.

 

Thanks again...

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I keep thinking I want to add a fuel flow meter/fuel computer to let me see what my actual fuel flow rate is.  Then I see threads like this and say to myself:  "Ignorance is bliss!"   :D

 

Was thinking the exact same thing!

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I keep thinking I want to add a fuel flow meter/fuel computer to let me see what my actual fuel flow rate is.  Then I see threads like this and say to myself:  "Ignorance is bliss!"   :D

 

Each additional doodad is an additional thing to fail and troubleshoot and repair.

 

Sometimes simple is good.

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Each additional doodad is an additional thing to fail and troubleshoot and repair.

 Sometimes simple is good.

Can't get more simple than sight tubes.

I think CT once said, "If your sight tubes can see fuel . . . so can your engine."

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