major fuel probe related issue -- need help

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major fuel probe related issue -- need help

Post by agmolnar » Wed May 15, 2019 4:54 pm

Hello all,

I am experiencing a major issue that has more or less grounded my DA40 for the past 5-6 months, and resulted in the R/H fuel probe being replaced three times. At the outset (in late November), the plane has an intermittent R/H fuel gauge indication (occasional red-X). As you can imagine, not being able to find the root cause has been exceedingly frustrating, and I am turning to the forum to see if others have experienced the same and if so what was the eventual fix.

Here is the quick write-up from my mechanic:

The original probe was intermittent red "X". We replaced the probe with new 1/14/19, 2199.6.

The first replacement probe was in service until 1/25/19, 2201.4 (1.8 hours), where it became out of range. We found R/H static dischargers INOP based on suggestion from Neil Grant. Replaced both dischargers with new. Replaced probe with new.

The second replacement probe was in service until 3/27/19, 2215.8 (14.4 hours), where it became out of range. We tested bonding / static systems and found no fault. Probe replaced with new.

The third replacement probe was in service until 4/30/19, 2228.2 (12.4 hours). The probe was tested and found to have no output. Wiggling the wire was able to produce an output around 11 hertz, but only momentarily. We were not able to reproduce any hertz output after that. Bonding and static discharge systems normal.

Mechanic thoughts: The original probe was intermittent, but each time it was tested it was found within range. It was replaced based on experience, we encountered the same intermittent failure on another DA40 and replacing the probe solved the issue. Every probe subsequently installed has failed in a different way; two have become out of range and now the last one has no output. If the argument was made that the airframe is taking out the probes, why isn't the failure the same each time? Why was the original probe intermittent, but never out of range? More troubling, why is the current probe hard failing in a way that seems so mechanical?

Thank you all for attention to this-
2007 DA40.695
Oakland, CA
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Re: major fuel probe related issue -- need help

Post by Colin » Wed May 15, 2019 9:36 pm

When my fuel probe failed in my DA40 during the first 100hrs of my ownership it turned out to be water in the fuel tank. Sorting it out required removal of the wing and completely flushing the fuel tank repeatedly with AvGas. Then a new probe was installed, the O-ring on the fuel filler cap was replaced, and it was fine for the next 1,500 hours until I sold the plane.
Colin Summers, PP Multi-Engine IFR, ~2,600hrs
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N971RD DA40 G1000 s/n 40.508 (traded)
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Re: major fuel probe related issue -- need help

Post by Karl » Thu May 16, 2019 2:02 am

As Colin says water getting into the tanks can cause all kinds of issues with the fuel senders.
As part of an accident investigation on a DA40D we found that a large amount of water can become trapped in the tank which is not easily removable through the normal drain valve. Just to be clear the cause of the accident was not water in the tank.

The bonding system can also cause a lot of issues with fuel senders and avionics systems. Don't just to test the ground for the tanks but carry out the whole airframe bonding test. If any of the readings are getting close to the high end of the limit I would suggest trying to reduce them.

Loose sockets in connection plugs is another classic diamond electrical issue. Gently squeezing the sockets with small pliers to improve the connection can often help. See attached pic.
Alt connector 2.png
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Re: major fuel probe related issue -- need help

Post by Rich » Thu May 16, 2019 2:35 am

Also, it comes to mind, check the crimps where the conductors are attached to the connectors.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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