Fuel System OverPressure 912IS

Re: Fuel System OverPressure 912IS

by Paul Depperschmidt » 8 years ago

Paul Depperschmidt

4 53 156

Apologies for the delay in reply. International work travel is slowing me down.

I did not build it, but I think the sender is a gauge type. It is positioned after the pumps and prior to the fine filter. It is in a position to allow the bypass valve to work in case of an over-pressure. The Dynon gauge is looking at Fuel Pressure only as far as I know. If it is using the MAP, I am not aware of it.

Unfortunately the Dynon provided no additional information other than "land the plane". I have not used the download engine function yet. I used to do it on the Cirrus all the time. Looks like I need to figure that out.

Re: Fuel System OverPressure 912IS

by Bill Hertzel » 8 years ago

Bill Hertzel

13 1.95k 8k

If the sender has ONLY one connection to the Fuel line, it is a "Gauge" pressure Sender.
If the sender has one connection to the Fuel line, AND a smaller Vacuum Line going to the intake Manifold, it is a "Differential" pressure Sender.
If you have a Gauge Style Sender and it is Not being corrected for MAP pressure by the Dynon, you will be seeing pressures in the middle 30psi range at idle.

If the Dynon is calculating the Differential Pressure it may give intermittent erroneous readings during rapid throttle changes as it collects and recalculates the updated data from multiple sources with various update delays.
Change the throttle position and give it a second for the display to stabilize.

The fuel pressure system is extremely reliable. When it goes bad it is going to go terribly bad.
It can go Plus or Minus 10-15 psi before the engine starts losing power.

You may want to open the alarm window even wider to prevent you getting used to alarms that you will keep ignoring.
Determine a nominal number for your individual engine and give the alarm window 5-7psi of wiggle room.
You do not want to get used to it "Crying Wolf!"

---

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

Re: Fuel System OverPressure 912IS

by Paul Depperschmidt » 8 years ago

Paul Depperschmidt

4 53 156

Thanks again Bill,

Is there an absolute not to exceed number for the fuel system, assuming it is a gauge type? It would seem possible to simply set the red level to that number? Or is it system specific?

I would post a picture, but can't figure it out in this system.

Re: Fuel System OverPressure 912IS

by RotaxOwner Admin » 8 years ago

RotaxOwner Admin

59 1.6k 16.6k

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Re: Fuel System OverPressure 912IS

by Paul Depperschmidt » 8 years ago

Paul Depperschmidt

4 53 156

I thought I had things fixed. I took the fuel system apart and blew in the filter with minimal restriction. Put it all together and flew for around 3hrs. One pump w pressures a little over 44. With multiple stops/ starts. On my last short flight when leveling for cruise the rpms started running up on their own, the fuel pressure went up and the red “land the plane” warning came on. As usual when I land and restart the engine is fine.

The higher revs came up suddenly. It would seem that a fuel pressure increase due to blockage would not cause higher revs. If anything the revs would fall due to a lack of fuel flow. If something blocked an injector, would it cause this? No EGT issues seen, so not thinking it is likely. Maybe throttle linkage?

For curious minds have included images. And I cut the old filter to see what was i it. Pretty basic.

8BAD9164-E417-4776-B7E6-2EDDFD42B740.jpeg (You do not have access to download this file.)

57154D79-6529-4673-8A94-5F04293A54DF.jpeg (You do not have access to download this file.)

3EF10A19-EB72-4316-B023-D81836CB77DE.jpeg (You do not have access to download this file.)

5C2E7E0B-E517-4442-9743-2F8E7501C8EF.jpeg (You do not have access to download this file.)