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Drop of fuel pressure

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georg.stiller(at)arcor.de
Guest

Posted: Fri Feb 10, 2012 11:47 am Post subject: Drop of fuel pressure

Hi all,



I have a problem with dropping fuel pressure. It happened twice so far. Conditions were similar.



Conditions yesterday were: Rotax 912, 80 hp, 250 hrs, outside temp. minus 10 centigrade, carb. intake temp. with carb. heat minus 1,5 centigrade.



Fuel pressure after engine start, warm up and for about 30 min. flight at 4600 rpm was constant around 0,3 bar. Than fuel pressure started to drop and after about half a minute reached the red line of 0,14 bar. That's when I engaged the electric fuel pump. Pressure than increased back to just below 0,3 bar. 



I returned to the field, landed, had a break, checked the fuel pump visually and it just looked fine.



After half an hour or so I took off again, flew for 20 minutes and fuel pressure was in the specified range at about 0,3 bar without engaging the electric pump.



Fuel pressure gauge (type 'Skydrive') is of manometer type. A fuel line goes to the gauge, no external sensor involved.



Any help would be highly welcome.



Regards, Georg

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bob(at)fly-ul.com
Guest

Posted: Fri Feb 10, 2012 6:07 pm Post subject: Drop of fuel pressure

 	  Quote: 	
		  

I have a problem with dropping fuel pressure. It happened twice so far. Conditions were similar.


	


For what ever its worth.. welcome to the world of crappy Rotax 912 fuel pumps. I, and several other people I know experience similar things. Doesn't happen all the time, and often doesn't even happen twice in the same day. In my case, freezing is never an issue. My episodes appear to happen after a long time at cruise altitude, during a descent, and it appears to happen when I descend about 2000 feet below my starting altitude.



As you probably know, Rotax came out with "Version 3" of their fuel pumps just this past summer.



Now, do you have the "fuel return line" and all that stuff in your system?



This is not to say your fuel pump is the cause.. obviously, there are still plenty of other things that could be going on. But in many circles, it is known that these pumps are not fool proof.



--

Bob Comperini

e-mail: bob(at)fly-ul.com

WWW: http://www.fly-ul.com

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Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Fri Feb 10, 2012 7:37 pm Post subject: Re: Drop of fuel pressure

You need to find out first if the reading is real or a false reading. You need to place a mechanical gauge in line and see if it match's what you see in the cockpit. This is the only real way to diagnos your problem whithout playing hit and miss and throwing money at the problem and hoping you get a hit. You can make a $20 setup for this with a 0-10 psi gauge and some copper tubbing from the hardware store. Until you do this everything else is stricly a guess. Once you put a gauge on it it will tell you where the problem is.

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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

georg.stiller(at)arcor.de
Guest

Posted: Tue Feb 14, 2012 9:38 am Post subject: drop of fuel pressure

Roger, Ivor and Bob,

thanks for your guidance. 2.5 hrs. flying last weekend, similar conditions as before and...no problem at all. I will keep the forum posted.

Georg

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