Fuel Flow randomly goes to zero

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nathanda40
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Fuel Flow randomly goes to zero

Post by nathanda40 »

Happened to me on a flight recently, fuel flow was fluctuating between 9.x gph expected and then showing zero during a flight. Engine was running fine and fuel pressure was normal. Was at a higher power setting, suspected vapor lock, so I turned on the electric pump for a minute or so. Didn't observe the issue again.

Anybody else seen this? Obviously I suspect there may be a connection/contact issue. But very intermittent, so trying to decide what to do.
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Re: Fuel Flow randomly goes to zero

Post by haykinson »

I had this problem before. Check out viewtopic.php?p=85942#p85942 for the conclusion of my problem — this $30 fix was after well over $2,000 worth of attempts to get the fuel pressure sender cleaned, rotated with the oil pressure sender (same part), or replaced outright.
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nathanda40
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Re: Fuel Flow randomly goes to zero

Post by nathanda40 »

haykinson wrote:
Mon Sep 27, 2021 5:38 pm
I had this problem before. Check out viewtopic.php?p=85942#p85942 for the conclusion of my problem — this $30 fix was after well over $2,000 worth of attempts to get the fuel pressure sender cleaned, rotated with the oil pressure sender (same part), or replaced outright.
Thanks for troubleshooting this for me.... :lol:

I assume the fuel flow display receives its information from the fuel pressure sender then?
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Rich
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Re: Fuel Flow randomly goes to zero

Post by Rich »

nathanda40 wrote:
Mon Sep 27, 2021 5:40 pm
haykinson wrote:
Mon Sep 27, 2021 5:38 pm
I had this problem before. Check out viewtopic.php?p=85942#p85942 for the conclusion of my problem — this $30 fix was after well over $2,000 worth of attempts to get the fuel pressure sender cleaned, rotated with the oil pressure sender (same part), or replaced outright.
Thanks for troubleshooting this for me.... :lol:

I assume the fuel flow display receives its information from the fuel pressure sender then?
No. There is a different device. A vaned spinning wheel that is monitored by a hall-effect transducer. Both are mounted right at the fuel metering control.
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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Re: Fuel Flow randomly goes to zero

Post by Steve »

Rich wrote:
Mon Sep 27, 2021 7:23 pm
nathanda40 wrote:
Mon Sep 27, 2021 5:40 pm
haykinson wrote:
Mon Sep 27, 2021 5:38 pm
I had this problem before. Check out viewtopic.php?p=85942#p85942 for the conclusion of my problem — this $30 fix was after well over $2,000 worth of attempts to get the fuel pressure sender cleaned, rotated with the oil pressure sender (same part), or replaced outright.
Thanks for troubleshooting this for me.... :lol:

I assume the fuel flow display receives its information from the fuel pressure sender then?
No. There is a different device. A vaned spinning wheel that is monitored by a hall-effect transducer. Both are mounted right at the fuel metering control.
Exactly right. The fuel pressure transducer and the low fuel pressure sensor are mounted to the fuel control unit. The fuel flow transducer is mounted in the fuel supply line between the engine-driven pump and the fuel control unit (about 8 inches away, covered by fire sleeve). Your symptoms suggest an intermittent connection to the fuel flow transducer. There is a connector wrapped and hidden in the fire sleeve. I would check that first.
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Re: Fuel Flow randomly goes to zero

Post by haykinson »

My recommendation for troubleshooting order is:

1) Visually inspect the fuel sender. Detach it, clean the contacts on the connector, clean the sender itself, reinstall. Problem might be temporarily fixed, so don't assume it's gone in one flight (could be a few months).
2) Switch the oil sender and the pressure sender. In G1000 installs, these are the same part — you will obviously need to clean the senders, but if the problem moves with the sender then you know it's the problem; otherwise, it's something else. Obviously be prepared for an oil pressure indication dropping to zero if it IS the sender.
3) Look at the cabling (including, as in my photo, inside the cabling). Intermittent problems consistent with a position and not with a sensor suggest some sort of a cabling issue.
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Re: Fuel Flow randomly goes to zero

Post by Stuart »

Diamond quoted $3300 for the oil sender in my 2007 DA40XL. Any better options?
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Re: Fuel Flow randomly goes to zero

Post by Steve »

Not sure about the sensors in the G1000 airframes, but on my VM-1000, the sensors are made by Honeywell. They still are not cheap, but as I recall, they were several hundred dollars (vs several thousand), and available from places like Mouser, DigiKey, or Newark. If you can get the manufacturer's PN (which should be on a sticker on the sensor), you will be able to source directly rather than buying through Diamond (with the shameful markup that goes along with that route).

Being a standard electronic component, there is no regulatory issue with doing this.
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Re: Fuel Flow randomly goes to zero

Post by haykinson »

If it's the oil pressure sender (i.e. same part as the fuel pressure sender) then I think the part is something like $1,200. Both the senders are pretty accessible, so it should be around an hour of labor in the worst case.
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Re: Fuel Flow randomly goes to zero

Post by Rich »

There are numerous replies here about fuel pressure sensors. The problem originally posted is about fuel flow, which is a separate and distinct type of sensor altogether. Ignoring fuel quantity measurements, there are three different sensors related to fuel delivery to the engine. Two of them might be interchangeable with their oil pressure analogs but the fuel flow sensor has no such equivalent.

My fuel flow indication has been known to temporarily indicate surges to substantially higher values while cruising at higher altitudes with no independent indication of cause or effect (sense of power change, EGT, CHT, fuel pressure, etc.). These surges would be a sudden increase to maybe 14-15 GPH then a slow decline (maybe ten second duration) back to normal. Without full knowledge of the fluid dynamics inside the flow sensor I attribute it to some sort of small vapor bubble somehow getting into the flow coupled with reaction to the signal by the VM1000. The other possibility is some sort of electrical gremlin influencing the communication between the sensor and the VM1000.
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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