Fuel gauge display is intermittent

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greg
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Fuel gauge display is intermittent

Post by greg »

For the last few flights I've made, the the left fuel gauge reading has been intermittent. The fuel remaining will vary, over a period of a few seconds, from full to seemingly random values (anywhere from 0 up), and sometimes display the red X. This first started after it had been left unflown for about two months with almost empty tanks, so I initially thought the sensor might have dried out, but since then the tanks have mostly full.

My observations:
- This is a 50 gallon plane, with G1000. The fault doesn't seem to be related to just one of the two sensors - with a full tank, it's just as likely to show between 20 and 24 gal as between 0 and 15.
- It doesn't ever seem to overread. If the tanks are half full, it'll vary between empty and half, never more.
- It seems to get better the longer the flight is. After an hour or so, the reading seems to stabilise and read what I expect to see. Whether this is due to temperature issues or due to the tank being emptier, I'm not sure.
- It will also happen on the second flight of the day, but there's always been at least an hour between flights - I've not been able to see what happens after a quick "refuel and go".
- On at least one occasion, the red X appeared right from startup, though it cleared before the run-ups were complete. (I didn't notice any issues for the rest of that flight. This led me to blame the long period of siting empty as the culprit, and gave me the misplaced confidence to take the plane half-way across the continent the following week :roll: )
- I've also been having problems with the autopilot, so I'm not ruling out an electrical system problem, but they started at different times.

Does anyone have any suggestions on what to look for? I'm getting no clues from the AMM. The wings need to come off in October anyway for the fuel hose replacement; should I be ordering replacement probes now and replace them while access is easy?
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Rich
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Re: Fuel gauge display is intermittent

Post by Rich »

You might want to price the fuel probes first. Just saying.😁
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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BRS
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Re: Fuel gauge display is intermittent

Post by BRS »

Greg,
What year 40 is this? What environment is it in on the ground (hangar, ramp, humid near the coast, dry in the desert).

So to reiterate, you are saying that both fuel probes on the left wing seem to be affected. If so...
- Either both probes have been contaminated in someway (unlikely but possible). Or..
- Something else in common to both probes has been affected.

Without searching out a wiring diagram, Several items come to mind, none of which involve pulling the wings off. BTW - if you do resort to pulling the wings off please don't try it in flight. OK, poor humor aside.

- Possible ground wire. Could be a poor crimp in a connector, corrosion between two connectors.
Search out these connectors and re-seat them.
- Issue with the box (name escapes me at the moment) that is responsible for interfacing airframe to avionics.
Could be internal or again, a connector. Start by finding and re-seating the connector.

Q. If you fly two days in a row (or morning then afternoon) are you less likely to have an issue the second flight compared to several days of not flying?
40.649 Sold (Still miss the DA40 from time to time)
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greg
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Re: Fuel gauge display is intermittent

Post by greg »

BRS wrote: Sun Aug 25, 2019 10:43 pm Greg,
What year 40 is this? What environment is it in on the ground (hangar, ramp, humid near the coast, dry in the desert).
It's a 2007, and for the last five years (since I've owned it), it's been parked on grass inland (not desert-dry, but not in the tropics either). But it did spend about spend about seven months last year AOG in a very windy, salty area, and there was quite a bit of surface corrosion on the exposed metal. So your suggestion about a bad connection is worth looking into. Wiring diagram, here I come...
- Possible ground wire. Could be a poor crimp in a connector, corrosion between two connectors.
Search out these connectors and re-seat them.
- Issue with the box (name escapes me at the moment) that is responsible for interfacing airframe to avionics.
Could be internal or again, a connector. Start by finding and re-seating the connector.

Q. If you fly two days in a row (or morning then afternoon) are you less likely to have an issue the second flight compared to several days of not flying?
So far, I've seen little evidence of it getting better with repeated flights.
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Colin
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Re: Fuel gauge display is intermittent

Post by Colin »

The symptoms you are seeing are what I saw when my DA40's right tank had water intrusion and the probes got rusty. They tried three times to fix it and ultimately had to replace the probes, which involves removing the wing.
Colin Summers, PP Multi-Engine IFR, ~3,000hrs
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