Fuel System OverPressure 912IS

by Paul Depperschmidt in 912iS Technical Questions 6 years ago

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Re: Fuel System OverPressure 912IS

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.96k

Are you getting a "Lane" warning light from the engine?
Download the logs from the Dynon and the engine ECM.
Look at the data closely. The cause of the problem is in there.

When the issue occurs; have you tried cycling the throttle through its full range in flight?
Or do you just throttle back and land?
What happens to the fuel pressure when you throttle back?

Was the fuel filter replaced BEFORE last flight?
The fuel pressure sensor is measuring the pressure in the fuel line before the fine filter.
Its purpose is to give you an ear warning of a potential problem.
This does Not mean the fuel pressure in the fuel rail of the engine has changed.

Just asking the obvious...
In the Fuel filter picture; The fuel comes OUT the Port shown in the picture.
Fuel flows from the outside to the inside within the filter.
It is installed correctly.

You had a previous issue with the throttle cable binding.
It was never actually resolved, the problem just disappeared. It may be returning.
Throttle UP is produced by giving slack to the cable and having the throttle spring take out the slack by opening the throttle.
If there is a delay in the cable being re-tensioned, The throttle may open a little more at a later time.

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

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Re: Fuel System OverPressure 912IS

by Paul Depperschmidt » 6 years ago

Paul Depperschmidt

4 53 156

Are you getting a "Lane" warning light from the engine?
Download the logs from the Dynon and the engine ECM.
Look at the data closely. The cause of the problem is in there.

Yes, I am getting Lane A warning light when it happens. I will figure out how to get that information over the holidays.

When the issue occurs; have you tried cycling the throttle through its full range in flight?
Or do you just throttle back and land?
What happens to the fuel pressure when you throttle back?

I did not cycle to idle other than to land. But I did cycle it. And it seems the rpm's keep creeping up and I have to back off the throttle. After the initial run up the fuel pressure settles down to normal. About 44psi.

Was the fuel filter replaced BEFORE last flight?
The fuel pressure sensor is measuring the pressure in the fuel line before the fine filter.
Its purpose is to give you an ear warning of a potential problem.
This does Not mean the fuel pressure in the fuel rail of the engine has changed.

Yes, the fuel filter had been changed. I pulled the system apart and checked it prior to the flight but did not change the filter. I did not think the fuel pressure prior to the fine filter could change the pressure at the rails (other than starving them, which is not the case here), so you confirmed that.

Just asking the obvious...
In the Fuel filter picture; The fuel comes OUT the Port shown in the picture.
Fuel flows from the outside to the inside within the filter.
It is installed correctly.

Fuel comes from the pump to the manifold holding the gauge. From there it normally goes to the fine filter and then to the rails unless the pressure forces the safety valve open. In which case it will bypass the fine filter.

You had a previous issue with the throttle cable binding.
It was never actually resolved, the problem just disappeared. It may be returning.
Throttle UP is produced by giving slack to the cable and having the throttle spring take out the slack by opening the throttle.
If there is a delay in the cable being re-tensioned, The throttle may open a little more at a later time.

What you described is what it feels like is happening. The RPM rev is sudden and after I have settled the throttle. The friction knob is snug enough to not allow movement there. And a couple of times when the event happened my hand has been on it and it did not move. It feels like the throttle cable is bunching up right after the sleeve and after a few minutes it snaps out. I am guessing that would potentially mess with the fuel pressure gauge and start the alarms. Then everything settles out. And when the engine is restarted all is well. It just does not seem like fuel filter blockage to me. I am leaning to the throttle linkage as the issue.

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Re: Fuel System OverPressure 912IS

by Paul Depperschmidt » 6 years ago

Paul Depperschmidt

4 53 156

I think we may have found it. In the Kitfox forums a builder was seeing the bunching up of the throttle cable. The short story seems to be an over torque on the nut securing the throttle cable. It has to move freely or it will bunch up. Based on the evidence I think this is the culprit on my Kitfox. I will check it this week. Some pictures will help explain.

B707B3E8-E85C-4533-9007-8DE3435C0030.jpeg (You do not have access to download this file.)

D67495EC-16C7-4374-8491-1D174C706924.jpeg (You do not have access to download this file.)

C7BAACE2-76A1-402C-852D-3F982479CBFF.jpeg (You do not have access to download this file.)

6312BB3A-A3A0-43B1-BE9E-8DAA8957E472.jpeg (You do not have access to download this file.)

Thank you said by: RotaxOwner Admin

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Fuel System OverPressure 912IS

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