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alpinelakespilot2000

Well Known Member
While flying today I noticed my fuel flow reading zero a few times, sometimes for sustained periods. When I got back and downloaded my data, I noticed that I was getting those zero readings generally only at low power settings and when my boost pump was off; at higher power settings, or when I turned the boost pump on, the fuel flow seemed relatively normal. At all times during the flight the engine ran normally with no stumbling whatsoever.

I'm not sure this picture is readable, but in the top chart the green is manifold pressure and the blue line is fuel flow. The bottom chart's red line is altitude.

You might be able to tell that I did three touch and gos to start, then climbed to 8500' and cruised for a while, then descended to land. If you look at my first 2 touch and go's, for example, the fuel flow seems relatively normal while the power is in and I'm climbing to pattern atittude. However, once I pull some of the power at pattern altitude my fuel flow drops immediately to 0.0 until I take off again. The only exception is my third touch and go when I used the boost pump. There you can see that some fuel flow is indicated. Likewise, after cruising for a while, once I pulled power to begin my descent, fuel flow pretty quickly goes to 0.0, only picking up again when I put my boost pump on for landing.

33lcepg.jpg


Any ideas what might cause this? I have a floscan that I'm guessing is either faulty or has something stuck in the vanes. My floscan is between my fuel selector and my boostpump, so I'm wondering if it takes the extra suction from the boost pump to get the vanes turning at the lower power settings. Would that make sense? I don't think it is electrical, b/c on the Dynon if you lose an electrical connection, you usually get a 99.9 reading rather than a 0.0 reading. Kind of stumped here.

[Just to clarify, I was intentionally not using my boost pump the first couple takeoffs just to compare full power fuel flows with pump off versus pump on. Indicated f.f. changes with my transducer located where it is. It is one of the disadvantages of this location. It makes it a bit trickier to calibrate or use the fuel totalizer if you do a lot of pattern work where the pump is on most of the time.]
 
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Location of the transducer should not be a factor. My transducer has been located the same place yours is for over 20 years and works perfectly. Never seen a zero reading with the engine running.
Are you sure you're not looking at fuel pressure? It's not uncommon for fuel pressure to read zero at low pressures.
 
Mel said:
Location of the transducer should not be a factor. My transducer has been located the same place yours is for over 20 years and works perfectly. Never seen a zero reading with the engine running.
Are you sure you're not looking at fuel pressure? It's not uncommon for fuel pressure to read zero at low pressures.
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Thanks, but no, it was not my fuel pressure. Pressure was more or less reading normal. The blue line on the graph indicates fuel flow. You'll notice it is flat-lined down at the very bottom of the chart (at 0.0) in a number of places even though I still am producing significant power.

Also, I'm not blaming the location of the transducer. I'm just speculating that if I have a problem with my transducer, its location might be exacerbating the problem a bit.
 
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cln1owner said:
Steve, has it behaved this way since first flight, or is this behavior recent?
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Hi Nate. Just happened for the first time yesterday. Looking back through the last few data downloads from the Dynon seems to confirm this. In the past, fuel flows have always stayed more or less b/w 2 and 5, never dropping to zero while the engine is running.

(BTW, prop just came back from Craig and seems to be right on, maxing out around 2700. Looks like the top end at 8500' will be around164kts, though I haven't done any 3-way runs to confirm it yet. Still envy your ground adjustable WW! :eek:)
 
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If memory serves, there was a post in another fuel flow thread about needing to crimp the **** out of the factory supplied wire connections.

It may, or may not, have been referring to the particular sensor brand you have.
 
Thanks Bill. I'll put that first on my list to check all electrical connections. I had thought that the Dynon just reads 99.9 when there is a loose connection, but Dynon just told me that the fuel flow transducer is an exception to that.
 
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connections

Check all your wiring connections to the transducer, especially the ones FWF.

I had a similar issue with my RPM dropping off to zero intermittently

It is usually the simple stuff.

Gordon

N144GP
Lancair Super ES
 
alpinelakespilot2000 said:
Thanks Bill. I'll put that first on my list to check all electrical connections. I had thought that the Dynon just reads 99.9 when there is a loose connection, but Dynon just told me that the fuel flow transducer is an exception to that.
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It counts pulses, so an intermittent open on the white wire would read as zero pulses, and hence zero flow.

Probably the same for a lost power or ground on the red/black wires.
 
So far I have not tracked down any bad electrical connections.

What puzzles me is that my problems are very repeatable. Go to some power over 1800-1900rpm and/or turn on the boost pump and I will get what appears to be a relatively stable, and normal reading, (though every once in a while I get a temporary drop in indicated f.f.). If I drop below 1800 rpm and/or turn the boost pump off, I get a 0.0 reading or something really close to that. In either case, the engine continues to run normally.

To me, the repeatability of this seems to indicate more of a transducer problem than an electrical problem. Is my logic good here? Just trying to figure out how much time to spend trying to track down an electrical gremlin if the problem is more likely the hardware.
 
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Pulled the transducer, tapped it lightly, sprayed some carb cleaner through it per the suggestion of another thread, gently blew through it, reinstalled it and all seems to be normal again. I'll update if my "fix" doesn't last.
Thanks for the help.
 
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