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h&jeuropa
Joined: 07 Nov 2006
Posts: 650
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 Posted: Sat Jul 31, 2010 5:23 am Post subject: 914 Fuel Press |
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On the 914 installed in our Europa we have a differential pressure gauge connected to the airbox and the fuel supply to measure fuel pressure as specified by Rotax. It has worked fine for over 150 hours. During the last 10 to 20 hours we notice the pressure varies during flight. It is nominally 3.5 psi as it should be but will increase up to 4.0 and decrease back to 3.3 or so. The change takes place over a few minutes and continues through the flight. The engine continues to run fine and all temperatures are consistent. The spark plugs look fine and all look the same.
With our Condition Inspection coming up we're curious if anyone has any ideas of things to check.
Jim & Heather
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kevann(at)gotsky.com
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| Posted: Sat Jul 31, 2010 7:47 am Post subject: 914 Fuel Press |
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Have you checked your fuel filter? Have you tried changing from main to
reserve?
Mine stays pretty consistent, changing with power setting.
Kevin, 914 with 220 hrs
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rparigoris
Joined: 24 Nov 2009
Posts: 805
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| Posted: Sat Jul 31, 2010 8:39 am Post subject: Re: 914 Fuel Press |
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Hi Jim
Differential pressure really won't have very much effect on mixture unless you are so low jets begin to suck air because fuel is not covering them or so high that pressure overcomes ability of needle valve to hold it back.
Rotax says between ~ 2 and 5 PSI over airbox is enough to overcome but not over do it. On the high side many folks with parallel pumps blow right over the high side when both pumps are switched on with out too much of a problem.
Can't speak from first hand experience, but if something changes it is worth a look into.
Here are some ideas:
**Gauge that is speaking with forked tongue. First off make sure senders have a good ground, running a ground specific wire to senders is a good idea in my book. There is always the chance that a sender has become irregular. Remember you have some very old gas in the line going to the fuel transducer. If it is mogas it could gum up. I plan to first fill this line and purge air from it using 100LL which is more better for not gumming things. May be worth a call to UMA to see if there is a cleaning procedure for sender and clean it, then purge it and run a ground specific wire from it.
**Perhaps there really is fluctuation happening. Go over vacuum/pressure lines with a fine tooth comb, a small leak here could be doing you in, pinched hose same problem.
**For hahas make sure your fuel tank vent is clear
**Make sure your fuel filters or gasculators are clean and there are no leaks. Leak could allow air to get sucked in
**Perhaps you imported some dog hair from Bob H. and it is clogging toe fuel outlet on tank? Does it happen on main and reserve? report back
**Make sure you have a good ground going to your instrument
**You didn't mention if pump 1, pump 2 or both pump one and two changes things, report back
**If sender/transducer is working perfectly, gauge is working perfectly and plumbing is in order, it could always be the fuel pressure regulator. There is an adjustment on it, you could fool one way and the other a little bit and see if it helps. You may want to check with Bud or Lockwood to see if there is any magic goop to run through it if you use a lot of mogas
**You still may have a plumbing leak, worth it to replace float bowl gaskets especial if you dropped float bowls to clean in there. There are other carb components that could have a potential leak going on but I think following through on above is a good place to start.
I would be alot more worried if you see pressure hitting the low end.
Perhaps you could borrow a fuel pressure regulator for testing?
I think you just had a pump burn out on you, again try both pumps, perhaps the new pump is a bit flaky? There is a break in, did you fly it at least half a dozen hours? Perhaps there isn't full voltage going to pump because of a high resistance connection?
Good luck
Ron P.
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