Low Fuel Pressure Warning (G1000)

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Droid
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Low Fuel Pressure Warning (G1000)

Post by Droid »

We just acquired this wonderful machine a couple of weeks ago, so I've only put about 4 hours on it so far myself. Today, in relatively normal conditions, I got a low fuel pressure warning. I instinctively kicked on the pump and it cleared in about 5 seconds. Never came back on. Never had any engine roughness or anything like that.

Being the data scientist that I am, I pulled the card and went to work. I can find several times over the past few years (including twice today) where the fuel pressure dipped for a few seconds. Today was just one of the few times it did it enough to trigger the alarm at 14 psi. In fact, it dipped like that 9 times when my partner was ferrying it home last week. He just never knew about it because it never quite got low enough to sound the bell, but it got close.

Some searching on here leads me to believe this may be, somehow, a normal thing, and that kicking on the pump is exactly what you do about it.

Is this a common thing for this airplane? The fluctuations in fuel pressure?
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Re: Low Fuel Pressure Warning (G1000)

Post by Pilot55 »

This is vapor lock usually on a DA40. Mine did this many times 5000 ft and higher. When this happens turn on the electric pump for a few seconds.
I now have a Lancair ESP with TSIO-550E. This engine tends to vapor lock at 10K and higher. I run the back up pump on low and never have a problem.
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Re: Low Fuel Pressure Warning (G1000)

Post by Droid »

Pilot55 wrote: Fri Oct 23, 2020 3:33 am This is vapor lock usually on a DA40. Mine did this many times 5000 ft and higher. When this happens turn on the electric pump for a few seconds.
So looking at the data, it looks like it's done this quite a few times, just never quite this low, and that it always just resolves itself within 10-15 seconds. Forgive my ignorance, but if I didn't run the pump, would I be right to assume it would have fixed itself this time as well? Or is it the other way around, and I should be watching that needle more closely and kicking on the pump whenever I see a drop?
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Re: Low Fuel Pressure Warning (G1000)

Post by nrenno »

I have owned a 2005 DA40 for 8.5 five years. After flying about 800 hrs in it I have never encountered this problem. Thus, I would say it is not normal.
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Re: Low Fuel Pressure Warning (G1000)

Post by Rich »

Over 18-1/2 years I have spent spending considerable hours 10,000 ft+. And for the last 5-1/2 years I almost never cruise below 6,000 ft. (Terrain around here is 3000 ft+.) I have noticed this low fuel fuel pressure event exactly once. More common, at altitude, I would see an unexplained significant increase in indicated fuel flow. Typically this would be jumping from ~10 GPH to something like 13, slowly backing down to normal over an extended period, perhaps 10-15 seconds.

However, these events were never accompanied by a variation in EGT, CHT or observed cruise speed. I chalk it up to likely occasional fuel vapor bubbles occurring in the fuel flow that influence the instrumentation but don't materially affect engine operation.

I have different engine instrumentation but an otherwise identical fuel system to the G1000.
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: Low Fuel Pressure Warning (G1000)

Post by Droid »

Rich wrote: Fri Oct 23, 2020 2:35 pm More common, at altitude, I would see an unexplained significant increase in indicated fuel flow. Typically this would be jumping from ~10 GPH to something like 13, slowly backing down to normal over an extended period, perhaps 10-15 seconds
This also happened immediately following the alarm. The POH suggests this is part of what happens, so maybe it happened to you relatively frequently too, just not enough to trip the alarm?
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Re: Low Fuel Pressure Warning (G1000)

Post by Rich »

Droid wrote: Fri Oct 23, 2020 3:33 pm
Rich wrote: Fri Oct 23, 2020 2:35 pm More common, at altitude, I would see an unexplained significant increase in indicated fuel flow. Typically this would be jumping from ~10 GPH to something like 13, slowly backing down to normal over an extended period, perhaps 10-15 seconds
This also happened immediately following the alarm. The POH suggests this is part of what happens, so maybe it happened to you relatively frequently too, just not enough to trip the alarm?
Possibly. In my plane the alarming activator is a simple mechanical pressure switch and might require lower pressure to trigger.
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: Low Fuel Pressure Warning (G1000)

Post by Rich »

When these low pressure warnings occur, has anyone checked what the actual reading is? The alarm annunciation is a consequence of how the low-pressure sensing switch has been manufactured. The actual minimum fuel pressure for the engine is documented by Lycoming at 14 PSI, though this is at the injectors. I'm not sure what the set point for my VM1000 is, but when I've experienced the bump in fuel flow, I didn't notice the fuel pressure gauge blinking, which is what it would do if it were below the minimum set point. This is what it does in the initial state before starting, of course. I didn't think to notice the fuel pressure reading itself.
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: Low Fuel Pressure Warning (G1000)

Post by Barry »

Dont mean to be a wise guy, but this is covered in your POH. I recommend you read it.. Vapor bubbles can occur in the fuel lines and will set the alarm off. I see it sometimes above 7K feet. I don't run my fuel pump however at higher altitudes because these pumps have a high failure rate.

"7. Electrical fuel pump ON at high altitudes

CAUTION

Operation at high altitudes may cause vapor bubbles,
resulting in intermittent low fuel pressure indications,
sometime followed by high fuel flow indications."
Barry Starkman
Commercial Instrument
DA40 N984ES 40.827
KEIK - Erie, CO
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