Fuel System OverPressure 912IS

[Jaguar56]

First significant post after purchasing an S7 w 912iS (N52LR) a few months ago. I have been putting some good flight time in and getting comfortable with the plane. Love it so far. I have been flying since 79 with time in many planes, but primarily an SR22 I sold a few months ago. I really like this kind of flying.

A couple of weeks ago shortly after takeoff I got a fuel high pressure warning. At the time I had the main pump running and full power. I throttled back and it bumped up to the red and the Lane A light came on solid. Shortly after the Dynon suggested to land the plane. I was not far from the runway and landed without incident.

I was able to communicate with the builder and review the fuel system. The filter system is relatively new based on the recommendation from Kitfox/Rotax. It was installed in March of this year and has somewhere near 30 hrs on it.

I found what looked like an oil drip coming from the fuel pressure sensor. I was able to pull both fuel filters. It was kind of a mess, could not figure out how to drain the system to keep everything from leaking when disconnected. I let the large post pump filter drain as best I could and captured the fuel. There was some very fine particles suspended in the fuel. I lightly blew in the end and it held pressure for a couple of seconds then gave way. It seemed clear after that. I could not see a way to open the filter. When pulling the pre-pump filter it looked pretty clear.

I put everything back together and checked the pumps. Everything seemed to be fine. The pressure holds around 44-45. I did a full power start / roll out and pulled the cowl. No leaks. Then took it up in the pattern for 20 minutes. All good.

With all that said I have a few questions for the experts.
1) Should I replace the post pump filter? Does anyone know the replacement?
2) That seems like a very short time for the filter to get stopped up, assuming that is the issue. Anyone else seeing this?
3) I am assuming the post pump filter is the source of the trouble. Anything else it could be?

How many have updated the filter system?

Thanks in advance for any help and support.

[efwd]

Put some funky fuel in it or have debris from the manufacture of the fuel system and one can plug a filter the day it is run the first time.
Kitfox part number for that 8 micron fuel filter is 98242.000 according to my 912iS FWF installation manual.
Eddie

[rosslr]

Hi Paul,

I have a 912is sport with the Kitfox FWF kit. I have 311hrs now and have changed out the fine filter 3x at the 100hr services. The fine filter I use is Genuine OE BOSCH 0450905021 / F5021 Fuel Filter

If you have the Kitfox fuel manifold, then when the fuel pressure increases to beyond the recommended pressure, it indicates that the fine filter is becoming blocked - however, the bypass valve will continue to supply fuel to the engine by bypassing the filter - a nice feature that gives you a pretty good margin of safety to land and change the filter out.

You have already found out that the course filter ( or pre pump filter) is able to be dismantled and cleaned whereas the fine filter ( post pump) is not serviceable - therefore you must replace it. I carry a spare.

Hope this helps

cheers

Ross

[Jaguar56]

Thanks for the feedback. That is what I was hoping to hear. I did study the system and figured out the bypass valve. That likely kicked in when the pressure shot up, but it was hard to tell. As you say it is nice to know the fuel flow won't simply stop. And it was interesting to see the Dynon tell me to land. That system is every bit the equal of what I had in the Cirrus.

I will just buy a few and have them ready when the pressure starts to work up.

[rosslr]

Yes Paul, I just order a few on line at a time and change them out ever 100 hr. I haven't had the prob you had but never know when you are going to pick up some rubbish in the fuel. And yes, the 912is system takes a bit of understanding and the warnings too. For instance, I went to start up recently and had a solid Lane B light - My EMS told me the EGT sensor was over heat ( although the engine was not running!) - obviously a sensor. Relatively easy fix ( expensive !) but what I didnt know and have since learned is that the EGT sensor info is not used by the computer to adjust fuel mixture - so it would have been fine to fly home if it happened somewhere. Apparently the system checks the injectors for that pot to make sure they are ok. I would carry a spare of them to but at $270 each I think that is a bit extreme!

good flying

r

[jiott]

Regarding the EGT sensor, if I haven't run the engine for 4-5 days when I startup the left side sensor almost always shows the red cross or a very high overtemp condition on my screen. I have learned to ignore it because in a few minutes of warmup it starts reading correctly and stays correct for the rest of the day. I have taken it out and cleaned it and checked the wiring but it has continued to do this for several years now. Probably should replace it; the right side never acts up.

[neville]

I also have the Kitfox fuel filter manifold and new filter arrangement. I have had the fine filter become clogged and get the high filter warning. I change the filter and all is well. Like Rossir I keep at least spares on hand and on any cross-country trip I carry a spare filter and a spare EGT sensor.

[jdmcbean]

We do keep the filters in stock if you're looking for them.

[Jaguar56]

Thanks John, just ordered them yesterday.

[Jaguar56]

Regarding EGT's, it was a constant issue with the Cirrus. It got so bad that people started ignoring them. But it was easy to dismiss when the EGT would peg out and then drop back in a few seconds.

With the Cirrus it was a connection issue. The connectors were junk. There was a guy who offered a package to replace them. It would usually eliminate the problem.

On the Rotax do they simply fail or is it a connection?

[Jaguar56]

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?

[Esser]

Just thinking aloud, can you go to a larger sized filter rated for a higher flow rate?

[Jaguar56]

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?

[Esser]

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.

[Jaguar56]

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.

[Esser]

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

[rosslr]

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.

[neville]

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.

[Esser]

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

[Jaguar56]

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.

[Jaguar56]

HI Paul

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.

Good advice, I will reach out to John and post on the Rotax Owners site.

I tried the particular filter with and without the washers with the same result. There were no washers used when the system was built, so I did not plan to use them. When I replaced the filter it sealed up fine without a washer. Guess it was just a bad one.

[Jaguar56]

I owned my Cirrus SR22 for 7 years and don't recall ever talking about the fuel filter. It had fuel injection with 6 cylinders and a lot of fuel flow. I never had an issue. The size of the filter was closer to the one prior to the pump in the Kitfox.

Just wondering if the cure is worse than the disease here? Did we know there were issues with fuel filtering in the IS previously?

[Jaguar56]

Or is it possible that the warning levels are set too low on the Dynon for fuel pressure?

[Jaguar56]

For those curious minds, there are new parts to the puzzle.

Based on feedback from the Rotax Owner forum I adjusted my warning levels on the Dynon to a higher setting. The Red alarm is now at 50psi vs. 47. I was hoping that was it. But unfortunately it looks like I have something else going on.

I took the plane up to check everything and it was all fine for about 20 minutes of pattern work and so I started out to explore locally. With both pumps on the pressure was in the 45 range. A couple minutes after leveling in to cruise with an RPM of 5300 and fuel pressure of 45 I felt a surge in the engine RPM. I looked down and the RPM had yellow lined and the fuel pressure went to 47. The Lane A light came on and the Dynon warning to land came on. I did not see the pressure hit 50, but it might have for a second. There was nothing in the Dynon to say what had caused the warning. I had to continually pull the throttle back to keep from RPM running up. The pressure backed down to 45 with pump 2 on only. This was exactly the same as before I adjusted the settings the previous week.

This new information had me pull the cowl and take a look at everything. I specifically looked at the throttle linkage. Everything looked OK. As I worked the throttle the action was not smooth at first. The wire seemed to bunch up a bit and then snap to full open. I worked that a few times and did not see it again.

I am hoping this is a simple, mechanical thing. Of the big 3 / fuel / air / spark, it still seems to be the fuel. But I am not sure what to investigate at this point.

[rosslr]

Paul, what type of throttle cable do you have? From what you describe it sounds like it could be the throttle - I have a mc Farlane type and if the friction on the vernier is not tight it will creep forward and increase revs but not dramatically - it sounds like your kink in the cable could be a problem and need replacing. HOWEVER, that does not necessarily explain the Lane A light coming on. I am not expert but FWIW I would:

1. eliminate any possibility of a faultly throttle cable by ordering and installing a new one.

2. check all the spark plug leads are attached properly

3. Then suspect injectors - my understanding is that Lane A controls half the injectors and spark plugs and Lane B the other half.

Beyond that, I am clueless.

good luck

r

[Jaguar56]

14459

My throttle linkage. Hopefully the picture worked. It was not linked, just seemed to bend a little prior to going full throttle.

[Jaguar56]

Update. Last weekend I pulled the fuel system apart and checked the filter again. As I had done before I blew in the filter and there seemed to be no restrictions. I lubricated the throttle cable a bit and went up again. Using the pump 2 the pressure never got above 44.5. No alarms. Maybe it is happy again.

I was curious and cut open the old filter. Here is what is inside.

[Jaguar56]

I really thought I had it. Flew for around 3hrs with multiple stop/starts and no issues. Pressures on pump 2 stayed in the 44 range. Last short flight and just leveling in cruise at 1500 AGL the engine started to rev up, fuel pressure went up, Lane A light and “land the plane” warning came on.

It almost felt like the throttle snapped open quickly, it freaks the system out, then settles down. But the warning lights will stay on until I restart the engine.

Not sure what is going on.

[dcsfoto]

I have not done a first engine run yet But , I have a Stock Flight Systems EMU and the first thing in the manual is to hook up a analog fuel pressure gauge and set the offset up

I have a rotax fuel pressure sender and it is indicating 15 psi and I have not put fuel in yet

David Kelm
7SS 912iS

[Av8r_Sed]

Your Rotax sender sounds suspiciously like it's sensing atmospheric pressure rather than "gauge". Not a problem if the electronics adjusts for it.

[Jaguar56]

Your Rotax sender sounds suspiciously like it's sensing atmospheric pressure rather than "gauge". Not a problem if the electronics adjusts for it.

I am really starting to feel it is nothing so complicated. I flew for almost 2 hours on Friday with no issues. But I was very closely watching any throttle movements. I worked the throttle full stop multiple times prior to engine start and all throttle movements during flight were much slower than normal.

Considering how quickly the events would happen and then settle down I really think it is the throttle cable bunching up slightly and then snapping to full throttle quickly as the bunch straightens out. I did see this happen once with the cowl off while working the throttle. This would explain the sudden rpm change and the increase in fuel pressure as the engine suddenly asked for a lot more fuel. And it would explain the warnings to the system and things settling down quickly after the event. And it would explain why the rpms would go up without a throttle movement in the cockpit.

I will keep working it with this in mind and post here with findings.

[efwd]

Im glad your posting this stuff. I installed my throttle a couple weeks ago and right away noticed that when the throttle cable is pushed forward I can see the end thats attached to the throttle arm takes on an arched shape even without the arm being full throttle. The pivot point inside that arm that the cable is bound too is not free to swivel. Of course if you loosen the screw that holds the cable in you risk having the cable come free and then your wide open throttle until you shut down the engine. My cable is what directly in line with that throttle arm. I don't really know what needs to be done to correct it but having read your posts I realize maybe the engine vibration is not sufficient to keep it from binding up as I thought might be the case. Maybe thats a spot where the LP1 dry lube is needed.
Eddie

[jrevens]

Could you guys post close-up pictures of the linkage at the engine? That would be helpful.

[Jaguar56]

Could you guys post close-up pictures of the linkage at the engine? That would be helpful.
Post #26 has an image of mine. Let me know if you don’t see it and I will post again.

[Jaguar56]

Not having built the plane I am not sure how the spring mechanism works. As the throttle is pushed forward it seems to push the throttle lever. Is that action with or against the spring?

Looking at the throttle image I am betting throttle up is with the spring action while throttle back the spring will help close the throttle. Guessing this is a safety measure in case the throttle linkage fails it will close the throttle?

[efwd]

throttle at idle, full throttle which the spring assists, and the way it probably should be if the bushing rotated freely and not binding.

[efwd]

Thanks John, for inspiring me to get off the couch this morning and get in the shop.

[Jaguar56]

throttle at idle, full throttle which the spring assists, and the way it probably should be if the bushing rotated freely and not binding.
You nailed it. That is what I was seeing.

[efwd]

Actually, the spring IS a safety measure but the opposite than what you stated. It fails with the throttle open so that you can get to a landing spot. Take the engine off line for the approach.

[jrevens]

The cable "bushing" should absolutely rotate freely in the throttle arm. It looks like it either isn't installed correctly, needs a little "work", or it's a poor design.

[efwd]

Since the instructions did not call out a specific torque on the nyloc nut it seems I may have tightened it enough to cause the cable to deform the brass bushing. I loosened the nut 1/8 turn and it now floats freely. Fixed.
Eddie

[Jaguar56]

Will check mine as well. It could simply be over torqued.

Thanks for all the help and advice everyone. Hopefully this is the answer.

[jrevens]

Since the instructions did not call out a specific torque on the nyloc nut it seems I may have tightened it enough to cause the cable to deform the brass bushing. I loosened the nut 1/8 turn and it now floats freely. Fixed.
Eddie


That's better! :) As per Rotax, the throttle and choke cable connections should be tightened 8 to 10 in.-lbs.

[efwd]

Thanks John. I guess I overlooked the Rotax manual. It is odd to me that they use a nylock nut on an engine component.
Eddie