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  #11  
Old 09-26-2017, 09:18 AM
n518jh n518jh is offline
 
Join Date: Jan 2015
Location: Sun City West, AZ
Posts: 11
Default Me too

I am also having a new low pressure indication on my RV12. I have a switch for the electric pump, so I can see what the fuel pressure measures at different power settings. I get low fuel pressure warnings on the Dynon 180 if I turn off the electric pump with the plane in level flight at anything over 4800 RPM. A replacement engine pump didn't change anything, so I'm wondering what could be wrong; the sensors, the fuel lines, etc. Any suggestions beyond ignoring it and using the electric pump if the engine falters? Mark
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  #12  
Old 09-26-2017, 09:38 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by n518jh View Post
I am also having a new low pressure indication on my RV12. I have a switch for the electric pump, so I can see what the fuel pressure measures at different power settings. I get low fuel pressure warnings on the Dynon 180 if I turn off the electric pump with the plane in level flight at anything over 4800 RPM. A replacement engine pump didn't change anything, so I'm wondering what could be wrong; the sensors, the fuel lines, etc. Any suggestions beyond ignoring it and using the electric pump if the engine falters? Mark
The RV-12 fuel system was designed for both pumps to be operating at all times (the standard per plans build has no switch to turn off the electric pump in flight)

Depending on the fuel being used, OAT, etc., it is possible for the measured fuel pressure to go below the set limit if both pumps are not operating.
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  #13  
Old 09-26-2017, 10:05 AM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
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My my, Jim! Looks like someone needs their safe space!😝
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  #14  
Old 09-26-2017, 11:16 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,511
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Quote:
I get low fuel pressure warnings on the Dynon 180
How do you know it is telling the truth? The pressure sensors are notoriously inaccurate.
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Last edited by Mich48041 : 09-28-2017 at 05:28 AM. Reason: Corrected misspelling
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  #15  
Old 09-27-2017, 09:21 PM
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Phantom30 Phantom30 is offline
 
Join Date: Jul 2009
Location: Coeur d'Alene, ID/Casa Grande, AZ
Posts: 563
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Quote:
Originally Posted by Mich48041 View Post
How do you know it is telling the truth? The pressure sensors are notorious inaccurate.
These fancy electronic systems are fantastic; and after seeing 2.3 or 2.4 psi with both fuel pumps operating during decent from altitude. I "wil be" installing both machanical fuel & oil gauges during next annual.

Call me insecure...but I start looking for someplace "immediately" to land when pressures are not what they should be. Likewise, an operational Garmin 796 w/remote gps...(had pito tube break @ clamp block) on way home from OSH loosing airspeed indication (nothing like landing with indicated 30 knot forward and 135 knot tailwind)..
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RV-12 Kit#729 "N312RD" is now a full functioning fun machine!! Thanks Van for fulfilling my dream😎
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  #16  
Old 09-27-2017, 09:47 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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Ric,

Disconnect it and enjoy the bliss of the ignorant!😜

Rich
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  #17  
Old 09-28-2017, 03:48 AM
thilokind thilokind is offline
 
Join Date: Sep 2007
Location: Montabaur, Germany
Posts: 64
Default Fuel Pressure Loss

I have a similar issue with my Zodiac 601 HDS with a Rotax 912 and leading edge wing tanks. Since several weeks the fuel pressure in cruise started to slowly drop from 5 psi to 2 psi (with the electrical pump and the mechanical pump running). When reducing RPMs the fuel pressure comes back. The situation has worsened over time; the fuel pressure now drops down to 2 psi during take-off. The engine runs without any issues, though.
I have tried almost everything: replaced the fuel pressure sensor (connected to Grand Rapid EIS), replaced electrical pump, replaced mechanical pump, replaced fuel hoses in engine compartment... so far no success.
I will now hook up a mechanical fuel pressure gauge.
Anybody with an idea about the root cause? I'm completely on a loss...

Thanks
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  #18  
Old 09-28-2017, 06:10 AM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
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2 PSI is equal to about 2 meters of head pressure in a gravity fed fuel system. That is plenty. The maximum pressure is set by an internal spring inside of the engine driven fuel pump. Pressure drop is caused by fuel flow. That flow can be to the carburetors, a leak, or return to the fuel tank.
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  #19  
Old 09-28-2017, 07:39 AM
Jolly Jolly is offline
 
Join Date: Nov 2016
Location: San Francisco, CA
Posts: 25
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Copy and paste from Rotax Owner forum:

"In the Installation manual it does say the re-circulation line restrictor is .35mm or .014".

Actually that is a misprint that should have been fixed. The restrictor should be a #35 Mikuni pilot or slow jet. It is actually based on fuel flow and not hole size from Rotax. The new pump really needs a re-circulation line or it can give erroneous readings and have high fuel pressure."
Looks like the .014 may work.

From what other 12 owners have told me that some 12 owners didn't use the restrictor in their re-circulation hoses. This allowed to much fuel to bypass and caused low fuel pressure and even engine stumbling at take off.
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  #20  
Old 09-28-2017, 08:35 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by Jolly View Post

From what other 12 owners have told me that some 12 owners didn't use the restrictor in their re-circulation hoses. This allowed to much fuel to bypass and caused low fuel pressure and even engine stumbling at take off.
Roger,
The RV-12 Rotax power plant kit comes with a pre-made hose that already has the proper restrictor installed. The only potential problem is if someone installs the hose backwards with the restrictor path routed to the fuel pressure sensor instead of the return line. It is rather obvious when this happens because the fuel pressure will not get into the normal pressure range with just the electric pump operating on the ground.
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RV-6A (aka "Junkyard Special ")
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