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Fuel Pressure Low

  • James Ott
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3 years 9 months ago #6765 by James Ott
James Ott created the topic: Fuel Pressure Low
I just completed my maiden flight in my Kitfox with a 912ULS. It is a new recent engine purchased in 2012 with the latest fuel pump installed. I also have the fuel bypass return option installed. The fuel pressure sensor is a Kavlico purchased with the Rotax 912 sensor kit from Dynon. My pressure readout is on my Dynon Skyview screen. The aircraft is of course a high wing with tanks in the wings and gravity flow to the inlet of the engine driven fuel pump. I do NOT have an auxilliary electric fuel pump.

Everything ran fine on the maiden flight, but during WOT climbs the fuel pressure would hover around the low pressure redline (2.2 psi). As soon as I leveled out in cruise it would be in the green at 4.0 to 5.0 psi. At idle to 2000 rpm it climbs to 6.5 to 7.2 psi. Should I be worried or is this range of pressures normal?

Jim

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  • Roger Lee
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3 years 9 months ago - 3 years 9 months ago #6774 by Roger Lee
Roger Lee replied the topic: Fuel Pressure Low
Hi James,

This is a little strange. My guess at this point is a bad ground connection (some Dynon's have their mounting bracket grounded too, a bad fuel pressure sender or even a poor performing pump. It would be helpful to put a mechanical gauge inline to check and see which one of these it may be.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last Edit: 3 years 9 months ago by Roger Lee.

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3 years 9 months ago #6802 by James Ott
James Ott replied the topic: Fuel Pressure Low
Roger, I will do what you suggest, but what is the "Normal" range of pressures I should see from 1800 rpm idle to WOT climbout?

Jim

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3 years 9 months ago #6804 by Roger Lee
Roger Lee replied the topic: Fuel Pressure Low
Hi James,

I believe the average fuel pressure with the new pump is 4.5 - 5.5 psi. It can vary slightly with rpm and if you run an auxiliary pump. Some do see pressures up at 6+ psi. That said many senders and gauges are known to be off and I do mean many. That's why if you think you have an issue then it is wise to put a mechanical gauge inline and double check the reading.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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2 years 7 months ago #9734 by neil hodgskin
neil hodgskin replied the topic: Fuel Pressure Low
Hi
I have a savannahvgxl 150hrs and have exactly the same problem.i have just fitted a NEW pierburg pump and have the same problem.i have an electric pump which I switch on with take off and it helps a bit. I have discussed this with many owners even the New Sling and all seem to have the same problem. They tell me to watch the fuel flow meter anf if the flow is constant then not to worry. I must say I am doing this and the flow rate stays constant without any drop.
I do not think anybody has the solution .I have tried pumps and guages and still the same and many others have the same.

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2 years 7 months ago #9739 by James Ott
James Ott replied the topic: Fuel Pressure Low
Neil, there is a much more extensive discussion of this subject in the "general Discussions" area. The thread title is "Low Fuel Pressure Alarm".

I agree nobody seems to have an answer for this. The factory appears to be ignoring it and pretending it is due to some faulty installation, but there are too many of us with the issue for that to be true. I personally believe the new fuel pump is weak and is just marginally able to do the job at WOT.

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2 years 7 months ago #9740 by Rob Seaton
Rob Seaton replied the topic: Fuel Pressure Low
Neil, how do you get a new Pierburg? they have not been available for over 5 years now.
The Pierburg did not have any pressure problems.

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2 years 7 months ago - 2 years 7 months ago #9742 by Roger Lee
Roger Lee replied the topic: Fuel Pressure Low
Hi Rob,

My Corona fuel pump that now has 150 hrs. on it has started to have low pressure (2.1 psi) on take off and then returns to 3.4 psi after a few minutes of flight. Then engine only has 150 hrs. too. Odd to say the least that this just creeped up while we have been having this discussion. My normal pressure was 3.8. I have a new pump in stock and may replace it to just take a look. Like others the engine never sputters, but I have done test with dead and disconnected pumps and the high wings seem to do very well with low pressures below 2 psi.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last Edit: 2 years 7 months ago by Roger Lee.

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2 years 6 months ago #9802 by Scott Church
Scott Church replied the topic: Fuel Pressure Low
I had the same problem after bringing my resale 2008 CTLS to Hawaii in May, 2013, and getting it in the air.

I called everyone back on the mainland, getting good suggestions, and over the course of a month or so I had put in the new fuel pump; changed some fuel lines; tried two new fuel pressure sensors. checked the connection to the Dynon.....Nada; same problem.

Finally, at the Oshkosh gathering that year with frustration from nobody being able to solve my problem, and having spent well over $100,000 to buy, ship, and re-assemble the CTLS in Hawaii, I spent about $100 for a new fuel pressure / distribution "screw" ( that sits atop the engine running through a small aluminum block where fuel lines disperse in various directions ) and "wallah", perfect 4.0 psi+/-.

So, what had happened? I will never know for sure, but apparently the problem related to this fuel pressure "screw" and a new one, which was fairly expensive for such a small part, solved my problem totally. And, I have not had any low fuel pressure "problem" indications whatsoever since.

Scott Church
Kona, Hawaii

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2 years 6 months ago #9804 by Roger Lee
Roger Lee replied the topic: Fuel Pressure Low
Hi Scott,

I believe the bolt you are talking about is the banjo bolt. If any debris had moved into the hollow area of the bolt then fuel pressures could be affected. Just by removing it you may have cleared it. Fuel pressure reading can be affected without fuel flow being affected, just depending on exactly where a piece of debris was. When having a fuel issue this is one area I always check especially after a hose change or if the fuel hose off the bottom of the fuel pump (pressure line out) was changed. Debris in the bolt could possibly move around and cause odd effects, but maybe too large to clear itself. I have seen this two other times.

p.s.

I also own a CT with 1200 hrs on it.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
The following user(s) said Thank You: Scott Church

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1 week 5 days ago #16424 by abdulla almazrouei
abdulla almazrouei replied the topic: Fuel Pressure Low
I do agree . I think the new mechanical pump is not pumping sufficient fuel . I do have a problem especially in summer . I had to change the fuel line and make the electric pump boost fuel in the mechanical. but whenever I switch the electrical pump off a sudden drom in the fuel pressure indication happens and followed by unintended engine shutdown.
I have low wing aircraft . its almost new with apx 50 hours.

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1 week 5 days ago #16428 by Roger Lee
Roger Lee replied the topic: Fuel Pressure Low
One thing I haven't seen addressed.
Is your fuel supply hose up to the fuel pump from the tank 1/4" or are they 5/16"? They should be 5/16" or the metric equivalent of 8mm. Then you can have a 1/4" from the pump to the fuel distribution block mounted on the balance tube.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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