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Thread: Rotax 912ULS Fuel Pressure Sender

  1. #11
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    Quote Originally Posted by John19 View Post
    On the topic of VDO senders I realise these are universally used, at least for Rotax installations, however I keep seeing a disclaimer on almost any VDO document as follows :- Warning Notice: VDO pressure senders are not to be used with any type of fuel application. VDO pressure senders may not be used in automotive braking systems. VDO pressure senders are not suitable for use in aircraft.
    I also note MGL talking about a "fuel isolation kit" for VDO senders.
    Do any Clanners have any information which specifically approves VDO senders for use with the Rotax? After all the original Oil pressure sender was VDO, albeit with a brass band.

    John
    I never got an answer on this question and cannot find a source of a "fuel isolation kit" if one is required. As I am about to put fuel in the lines it is about time for me to review this issue. Any help appreciated.

    John

  2. #12
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    Hey guys,

    My Rotax 912 ULS fuel pressure readings fluctuate between 1.5 and 6 PSI. It has been doing this since new (now 100 hours). The lowest PSI readings normally occur after switching off the AUX pump after take-off climb out. On a typical 90 minute flight the PSI might read in the 4s then 3s then 5s then 2s then 6s. The readings stay in each range for about 10 to 30 minutes and then take on a new range. Is it normal for the fuel pressure on a Rotax 912 ULS to fluctuate or stay steady?

    I have a Skyview panel with a Kavlico (100433) fuel sensor mounted in a block low on the fire wall connected by a 28 inch -3 hose to the 912 fuel tree on top of the engine.

    I am wondering if,

    1. pressure changes in the fuel pump vent tube might be causing an impact on the fuel pump diaphragm. I have the end of the vent tube in what I think is neutral air (not in the air stream).

    2. the 28 -3 hose is too small to allow the Klavico pressure sensor to measure the actual fuel pressure accurately.

    3. the mogas in the 28 -3 hose has turn to lacquer preventing an accurate reading. I am thinking of taking the hose off to sample the fuel inside.

    Any advice or thoughts would be appreciated.

    Thanks
    Mike Duggan

  3. #13
    Premium Member (Donated) s19flyer's Avatar
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    Mike,

    How is your ground wire configured? Is it run to the ground buss or the firewall?

    Do you have the restriction orifice in the line at the fitting on the fuel manifold? I don't

    I had the same issue and thought it had lacquer in it but it was radiant heat that was causing it. Moved it low on the firewall (as you indicated you did) and problem solved. Any chance it is still getting hot? Or the line to it is getting hot?

    Another test would be to switch to avgas and see if the problem corrects itself. If so, then it could be fuel boiling in the lines.
    Glenn
    Avid Flyer, S6ES, S19, S20 In Progress
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  4. #14
    Premium Member (Donated) s19flyer's Avatar
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    Oh yea,

    Go into your Dynon configuration setting and make sure the right fuel pressure sender is still selected. Somehow mine changed and was causing similar issues.
    Glenn
    Avid Flyer, S6ES, S19, S20 In Progress
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    Remember, I am not immune to mistakes!
    What works for me may not work for you.

  5. #15
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    Glenn

    Thanks for your helpful suggestions on my fuel sensor problem. I was going through your check list and noted that my Dynon EMS configuration was was set for a Kavlico model 101690 - 0000 (rated 15 PSI) but my paperwork for the kavlico I installed says it is a model 101716 - 0000 (rated 50 PSI). I need to double check my sensor model but 50 PSI sounds like it would be the wrong sensor for the Rotax. What kavlico models are other fokes using on their Rotax? I will correct the Dynon configuration to the 50 PSI model and see what kind of readings I get.

    Thanks
    Mike Duggan

  6. #16
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    Quote Originally Posted by MikeD View Post
    Glenn

    Thanks for your helpful suggestions on my fuel sensor problem. I was going through your check list and noted that my Dynon EMS configuration was was set for a Kavlico model 101690 - 0000 (rated 15 PSI) but my paperwork for the kavlico I installed says it is a model 101716 - 0000 (rated 50 PSI). I need to double check my sensor model but 50 PSI sounds like it would be the wrong sensor for the Rotax. What kavlico models are other fokes using on their Rotax? I will correct the Dynon configuration to the 50 PSI model and see what kind of readings I get.

    Thanks
    You should have the 15# one for the carb 912. The 50# one is for a fuel injected engine. I'm thinking that since your on the very low end of that sensor it's readings will be unstable.

    Now if I can get my CHT and EGT readings to read right on the Skyview in the S20 I'll be happy.
    Glenn
    Avid Flyer, S6ES, S19, S20 In Progress
    http://www.mykitlog.com/s19flyer
    Remember, I am not immune to mistakes!
    What works for me may not work for you.

  7. #17
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    Ooops, my mistake, it looks like I do have the correct fuel sensor - Kavlico model 101690 - 0000. Back to square one but eliminating possibilities.
    Mike Duggan

  8. #18
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    Hi Mike,

    Thinking outloud, do a search on your sensor, Kavilico model 101690. Could it be defective? That would be my first thought as it seems your plane has no other problems.

    Dale

  9. #19
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    Thanks Dale,

    A quick check shows that Dynon does have an advisory published about defective Kavlico sensors and some tests that can be completed to see if I have a defective unit.
    Mike Duggan

  10. #20
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    Mike,

    Just so others know, it maybe easy to tell if a sender is bad. Ground the sending wire and the needle will peg or the the display will. Always start with the easy things not with the hard ones....such as fuel and fuel lines.

    Dale

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