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  #1  
Old 04-16-2014, 09:28 AM
johns4689 johns4689 is offline
 
Join Date: Sep 2010
Location: Myerstown, Pa
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Default Fuel Pressure

I just had my second fuel pressure sending unit go bad. Before you ask, yes, I have it mounted on the fire wall. Does anyone have a good reliable model that works well on the Rotax?
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  #2  
Old 04-16-2014, 10:45 PM
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ScottSchmidt ScottSchmidt is offline
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What happens when they go bad?
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  #3  
Old 04-17-2014, 05:59 AM
johns4689 johns4689 is offline
 
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Location: Myerstown, Pa
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Default Fuel Pressure

When mine fail my fuel pressure drops very low. I installed another pressure gauge in the line and I still have good pressure, but my Dynon shows only 1.5 to 2.0 lbs. I replace the pressure sensor and the Dynon reads good again.
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  #4  
Old 04-17-2014, 07:30 AM
roger lee roger lee is offline
 
Join Date: Sep 2013
Location: Tucson, AZ
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What pressure sender are you using? Location can make a difference. Is the pressure sender behind any exhaust pipe, muffler or exhaust outlet? If it is you can reduce the heat affect by wrapping the exhaust pipe. Heat will cause an untimely death. When mounting to the firewall use some type of vibration isolation if possible. When mounting the pressure sender on the firewall it is better when it is slightly higher than the balance tube for the carbs. I have been using the same fuel pressure sender for almost 6 years without any issues, but it is mounted on the firewall, high to drain fuel away from it when sitting and vibration isolated.

That said you can get a bad sender from time to time.
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  #5  
Old 04-18-2014, 06:50 AM
johns4689 johns4689 is offline
 
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Location: Myerstown, Pa
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Default Fuel Pressure

I'm using VDO sending units. I do have the units mounted high but the only thing I don't have is something to absorb the vibration. They are not mounted near any of the exhaust. When I use the mechanical gauge inline I am getting over 5 PSI. I'd like to a more reliable sending unit.
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  #6  
Old 04-18-2014, 08:02 AM
roger lee roger lee is offline
 
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Location: Tucson, AZ
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VDO senders have been used on the Rotax for a long time. That said they do go bad and mounting can be a major contributing factor.
There are other sending units on the market, but if you have the SLSA you would need an LOA from Vans. VDO's can be sensitive to vibration and that may be all that is killing yours.
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  #7  
Old 04-18-2014, 08:12 AM
mrt890 mrt890 is offline
 
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Location: Friday Harbor, Wa
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https://store.dynonavionics.com/cgi-bin/commerce.cgi

The 15psi Kavlico is what you are looking for. But it will require a small wiring harness modification.
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  #8  
Old 04-18-2014, 08:18 AM
roger lee roger lee is offline
 
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Location: Tucson, AZ
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Dynon have moved away from VDO to Kavlico. You can get more info from the Dynon site if need be. It is an easy change out with a small wiring modification. As Michael points out it would be a good swap.
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  #9  
Old 04-18-2014, 08:48 AM
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Bill_H Bill_H is offline
 
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Location: Marshall TX (KASL)
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From another thread:
If you intend to buy the new version fuel pressure sender,
Dynon part number 101690-000
Carbureted Fuel/Fluid Pressure Sender-Kavlico, 1/8-27 NPT, 15 PSI , $85
... don't get it from Dynon - they charge a $20 fee plus shipping. In fact they recommend that you use one of their retailers. Aircraft Spruce is one of them, their part number 10-04820, DYNON KAVLICO CARB FUEL SENSR, $83 plus $2 shipping by mail.
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  #10  
Old 04-19-2014, 05:14 PM
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WingedFrog WingedFrog is offline
 
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Location: Raleigh, NC
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My fuel pressure runs around 5 psi, at the top of the green and close to the yellow. I installed a switch to cut the electric fuel pump, mostly for not being bothered when I need the master on while in the hangar. A couple of time I cut the electric fuel pump in flight and was scared to see the fuel pressure drop to between 1 and 2 when operating with only the mechanical pump. I did not see any change in RPM (all this checked with savyyAnalysis) but it scared me enough to leave the electric pump on in flight. Note that with the engine off the pressure from the electric pump reads 3.7 psi, consistent with the mechanical pump of 1 to 2 for the total around 5. My question: is it normal to get such a low pressure from the mechanical pump alone? I don't remember seeing this behavior in the Sportcruiser in which we systematically stop the electric pump outside the take-off or landing phases.
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