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  #1  
Old 08-14-2021, 09:53 AM
Mountain Time Mountain Time is offline
 
Join Date: Apr 2012
Location: Puget Sound
Posts: 82
Default G3XT - Wandering Fuel Flow Readings

Over the last few flights I've noticed the fuel flow on my G3X Touch having frequent periods where it wanders all over the place during cruise - for example, where I should be at a steady 8.8 GPH or so, it will trend down to the low 7 or high 6 range, then trend back up into the 9s, etc. This happens quickly - you can see it quickly flicker through the range, up and down, in just 10-15 seconds (ballpark) or less. There's no apparent rhyme or reason. And the other engine data are normal and the engine runs as though there is nothing abnormal happening.

Other times it will settle in and stay in the expected spot, maybe varying .1 or .2 GPH depending on whether the engine loads up a bit as the autopilot works to maintain altitude in a slight downdraft , as an example. That's the normal behavior I'm used to seeing.

The sender is a FloScan 210 from when I built the plane with the RMI uMonitor and has 700 hours on it, about 150 of that with the G3XT. And, the interesting thing is that the total fuel used still comes out on the money (or dang close) when its time to fill up, as it always has. So that doesn't seem to be affected.

Any ideas from the collective mind? I haven't dug into anything yet but wanted to see if there's something specific I should be looking for.

Thanks in advance -

John
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  #2  
Old 08-15-2021, 03:13 PM
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Thermos Thermos is offline
 
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Location: KASH
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Default

I'm not an expert on the FloScan but I'd suggest checking the easy things first, like wiring. An intermittent fault like that is often caused by a bad ground or loose connection.

The G3X's fuel totalizing function is sampling the FloScan's output pretty quickly, probably 1/second. An erroneous flow indication over a few seconds isn't going to make a noticeable difference in the total fuel used. 0.5 gph error divided by 3600 seconds/hour is a pretty small number!

HTH

Dave
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  #3  
Old 08-16-2021, 01:15 PM
Mountain Time Mountain Time is offline
 
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Thanks Dave, that mirrors my initial thinking - I don't think there is much to the FloScan physically, a paddlewheel and pulse counter/generator inside the unit, and the wires to same. So likely either a connection issue somewhere, or something going flaky inside the FloScan itself, which would mean toss it out and replace.

John
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  #4  
Old 08-16-2021, 09:11 PM
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Planecrazy232 Planecrazy232 is offline
 
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Location: Cape Coral, FL
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My 0360 has always done that on my G3XT. I attribute it to the carb float opening and closing. Very rarely it is steady.
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  #5  
Old 08-17-2021, 07:24 AM
lr172 lr172 is offline
 
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If the reading is always erring on the low side, I would suspect the paddle bearings in the floscan are failing. As the bearing creates drag, the moving fuel is read as lower than actual, due to having to overcome drag. On the Red cube, these are jewelled bearings with very low friction and expect floscan is the same.

Only use red cubes, but 700 hours seems to be a pretty good run for them. I have yet to see one last longer than 750 hours.

Larry
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Last edited by lr172 : 08-17-2021 at 07:28 AM.
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  #6  
Old 08-17-2021, 08:43 AM
TS Flightlines TS Flightlines is offline
 
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This sound familiar-------

Tom
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  #7  
Old 08-17-2021, 09:33 AM
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Longez Longez is offline
 
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Location: KS
Posts: 261
Post Carburetor Cleaner

I have a Floscan 201B connected to the G3X Touch system in my plane.

Every 3 to 4 yrs it starts to read erratically and generally lower than it should and sometimes the vane even stops turning and it reads zero.

I remove the fuel lines on both sides of the flow sensor, and as gently as possible, spray carburetor cleaner (no compressed air!) in from both sides. Re-attach the fuel lines, and everything is back to normal.

I have had to do this a couple of times in over 10 years of using it.

Steve
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  #8  
Old 08-17-2021, 01:14 PM
Mountain Time Mountain Time is offline
 
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Quote:
Originally Posted by TS Flightlines View Post
This sound familiar-------

Tom
Well, don't be coy Tom - what are you thinking?

I should mention that the variation is both up and down, i.e., higher than actual as well as lower than, although I'd say I see more on the lower side than above.
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  #9  
Old 08-17-2021, 09:53 PM
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czechsix czechsix is offline
 
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Location: Spring Hill, KS
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Quote:
Originally Posted by Planecrazy232 View Post
My 0360 has always done that on my G3XT. I attribute it to the carb float opening and closing. Very rarely it is steady.
Yeah same with my O-360/Floscan/G3X combo, however I typically saw +/-0.3 gph variation. In this case where the variation has become much larger, but the fuel totalizer is still accurate, I wonder if the carb float hinge or needle has developed excessive friction or become 'sticky' and isn't operating as smoothly as it used to. Can't say I've seen that happen but it's a mechanical device with moving parts so it seems plausible. If that turned out to be the cause, your flowmeter may be fine and you need a carb overhaul instead.
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  #10  
Old 08-18-2021, 07:15 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by czechsix View Post
Yeah same with my O-360/Floscan/G3X combo, however I typically saw +/-0.3 gph variation. In this case where the variation has become much larger, but the fuel totalizer is still accurate, I wonder if the carb float hinge or needle has developed excessive friction or become 'sticky' and isn't operating as smoothly as it used to. Can't say I've seen that happen but it's a mechanical device with moving parts so it seems plausible. If that turned out to be the cause, your flowmeter may be fine and you need a carb overhaul instead.
If that were the case, the fuel height in the bowl would be changing and changes in fuel height create changes in fuel delivery volume at a constant air flow. The OP would be seeing noticeable swings in engine performance if that were happening.

Larry
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