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Thread: Fuel System OverPressure 912IS

  1. #11

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    Default Re: Fuel System OverPressure 912IS

    Frustrating.... On Saturday I changed the oil, filter and the fuel filter. I had purchased 3 replacement fuel filters based on good advice here. The original filter seemed to be working OK, but it had a problem prior, so just to be safe (maintenance induced problem coming) I replaced it. A real mess any time the system is pulled apart as there is no way I can see to keep from a lot of fuel spilling. I put the system together with the new filter and checked for leaks. The entry point of the filter would not stop leaking. I tried multiple time to pull it apart and re-seat, no luck. So I pulled another new filter and put it in. It sealed. Threw the other away. The pressure on pump 1 was in the 45 range. Seemed a little high, but in the green. The 2nd pump would put the system in yellow. I flew the plane for a while, running on the single pump one. It ran fine.

    Yesterday I took my wife to Fredricksburg for lunch. All was well on the outbound trip. But 10 minutes in to the return the fuel pressure was in and out of yellow. Then it went red and Lane A light and the "land the plane" warning came on. My wife was concerned, but not seeing me get too worried helped her. I had to continually back off of the throttle to keep the RPM's down. I was close enough to my home airport to press on while keeping safety airports in range. I was able to land without a problem and on the ground turned the engine off and back on. The fault had cleared and the fuel pressure was back down to 44.5 or so. I noticed that using the pump 2 rather than 1 brought the pressure down to the middle range. Both pumps on would hit the yellow.

    So... I am thinking the filter I had originally been running in the plane may have failed allowing the pressure to go down. The new one seems to just be too fine to allow proper flow. Yes, I could have accumulated trash in that short of time (1hr). But considering I effectively flushed the system multiple times by taking it apart, does not seem likely.

    I could just run on pump 2 at the lower pressure and likely be OK. But this just does not seem to be working right. As a safety measure the fuel filter seems to be causing in-flight problems more than solving them. Any one else seeing anything like this? Suggestions?

  2. #12
    Senior Member Esser's Avatar
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    Default Re: Fuel System OverPressure 912IS

    Just thinking aloud, can you go to a larger sized filter rated for a higher flow rate?
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  3. #13

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    Default Re: Fuel System OverPressure 912IS

    Quote Originally Posted by Esser View Post
    Just thinking aloud, can you go to a larger sized filter rated for a higher flow rate?
    I was thinking that might be an option, but not sure what would work.

    Possibly backing off the fuel pump pressures? Are they adjustable?

  4. #14
    Senior Member Esser's Avatar
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    Default Re: Fuel System OverPressure 912IS

    I admittedly know very little about the 912iS but backing off the fuel pressure isn’t a great idea due to the fact that your injectors need a certain pressure that will be regulated by your fuel regulator.

    Your filter would before all this stuff so lowering the fuel pressure would lower it even further after the filter which may not deliver enough pressure to the injectors.

    In fact this is making me think of you have an adjustable fuel regulator to make sure it is set at the correct pressure or trouble shoot that it hasnt failed.
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  5. #15

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    Default Re: Fuel System OverPressure 912IS

    Thanks Josh. That is definitely a possibility as the regulator is downstream of the last filter. What leads me to the filter is that it was working before I replaced it. But it seems the pressure in the system has always been on the high side.

    Is there any issue with just running on pump 2? It seems to be running at a lower pressure to the filter.

  6. #16
    Senior Member Esser's Avatar
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    Default Re: Fuel System OverPressure 912IS

    Can you easily configure it to put your fuel pressure sensor on the other side of the filter? It would just be interesting to read the pressure difference between each side to see if the filter really is the problem.

    You really don’t want to find out your injectors aren’t getting enough pressure the hard way b
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  7. #17
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    Default Re: Fuel System OverPressure 912IS

    HI Paul

    I am overseas at the moment so a bit low to follow TKF threads. I have a 912is sport with about 320hrs on it now. What you describe is a bit baffling to me. I am certainly no expert but for what it is worth here are my thoughts.

    First, my fuel pressure always reads about 46/47psi on pump 1 at cruise. As you have noted, it will be higher with both pumps on but always cruise with just one. Although mine reads high, I put that down to a calibration issue that I cannot find out how to adjust - doesn't worry me as the fuel pressure is an indication of weather the fine filter is becoming clogged. So I use it as a relative gauge over time. That said, I have not had it creep up over the life of a 100hrly more than 1 psi. And even if it did, I understand it has to be really clogged to starve the engine - and then the manifold has a bypass to supply the engine - so rightly, I think you not being too worried about a small increase in flight was justified. But that doesn't explain why you had such a variation in the pressure readings with the different filters you tried. I too would assume contamination of the filter in the absence of any other theory!
    But I would post again on the Rotax Owners site under the 912is engine thread as there are some pretty wise Rotax heads on that site.

    The second issue about getting the fuel system to seal is worrying. Are you using the copper crush washers that were supplied? I think from memory they might be different sizes at each end of the filter but being away from home I cant verify that.

    Thanks for posting as I find that sharing our thoughts helps create some knowledge around this relatively new engine. Of course, John Mc is pretty experienced with this engine and the fuel manifold setup so it could be worth an email direct to him to ask his views too.
    Ross
    Mt Beauty, Vic
    OZ
    Sold to Richard and Scott Taubman in OZ, 2019. Kitfox SS7,Rotax 912is Sport, Airmaster CSP 75" blades.
    Landcruiser and Cub off road camper (doesn't get any kudos on this forum!)

  8. #18

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    Default Re: Fuel System OverPressure 912IS

    Admittedly The Mogas fuel at my home airport is at times somewhat contaminated because they run the tank to empty before ordering more fuel. So final filters do not seem to last very long. One interesting thing I have noticed is that when the fuel pressure goes into the high limit (49/50 PSI) I can see when the bypass check valve opens as the pressure drops to 40 psi.

  9. #19
    Senior Member Esser's Avatar
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    Default Re: Fuel System OverPressure 912IS

    Quote Originally Posted by Jaguar56 View Post
    Thanks Josh. That is definitely a possibility as the regulator is downstream of the last filter. What leads me to the filter is that it was working before I replaced it. But it seems the pressure in the system has always been on the high side.

    Is there any issue with just running on pump 2? It seems to be running at a lower pressure to the filter.
    I’m putting fuel injection on my aircraft and I’m only planning on running one pump at a time after checking them both during run up. I don’t think it would be an issue to only run one but i think I would put a fuel pressure sensor on each side of the filter so you can monitor differential pressure. You really really want to make sure your injectors are getting the specified pressure
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  10. #20

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    Default Re: Fuel System OverPressure 912IS

    Quote Originally Posted by Esser View Post
    Can you easily configure it to put your fuel pressure sensor on the other side of the filter? It would just be interesting to read the pressure difference between each side to see if the filter really is the problem.

    You really don’t want to find out your injectors aren’t getting enough pressure the hard way b
    Thanks Josh, it might be easy for someone, but not me. I was not the builder, so I don't have the skills necessary to do that. It might be possible to put a pressure gauge inline on the fuel hose that goes to the rail. I will think about that one.

    One thing that keeps me pointed at the filter, the engine never had an issue. The only problem was the high pressure in the fuel line.

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