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Another fuel pressure issue

M

Mark Henderson

Well Known Member
Off and on since my first start up I have had intermittent low fuel pressure alarms. In the last 20 hours of opperation I have had no problems. I just installed a UMA mechanical 0-10 PSI fuel pressure gauge. NO changes were made to the fuel system other than re-routing the fuel hose to the sender and putting in a manifold. The dynon sensor is mounted on the right side and an an-3 aeroquip hose ro the gauge on the other.

First thing I noticed is that the Dynon reads lower than UMA. With just the electric pump on the Dynon reads 0 but the UMA shows 2.5.

On start up the Dynon reads 1.8 and the UMA 4. 2 PSI . GPH is 2.2

After warm up at 3000 RPM the Dynon shows 1.5 PSI and 2.2 GPH. The UMA drops to 3.5 GPH

At 4000 RPM The Dynon is at .7-.9 PSI and 3 GPH. The UMA drops to 2.5 PSI.

There is no seepage that I can see from the fuel pump, nor is fuel leaking anywhere that I can see.

Any thoughts?
 
I had the same problem with my 9A.
Fuel sender lost most if not all of its "pressure" reading as the engine warmed up. Went to the same mechanical guage you did and pressure apparently had been good all along. Fought the problem for 6 weeks, 3 new senders, all on the firewall, all erroneous readings. 110 hrs with the mechanical no probs. Don't trust the senders. Not happy with my oil sender on the 9A either.

Doug, N79DJ reserved for my 12, waiting on skyview, FF forward finished
 
Don't trust the senders.
Click to expand...
I agree. The RV-12 fuel pressure sender is poor quality. The fuel pressure display should be treated like a pressure switch: Yes there is pressure, or no, there is no pressure. The actual psi value is meaningless.
Joe Gores
 
Try the Dynon Forum. Dynon was very helpful to me with my fuel pressure sender problems. They know the sender is not ideal but have not yet found one to replace it. They will work with you.

Jim
RV-12 #264
flying since 12-10
 
Fuel pressure on Dynon

Make sure you don't have air in the lines. I opened the pressure line at the firewall, turned the fuel pump on and re-capped the opening, and WALLA ! !
 
For all practical purposes, air in the line has no effect on the pressure. Fuel will enter the line and compress the air until the air is at the same pressure as the fuel. The fuel pressure sensor does not care if air or fuel pressure is applied to its diaphragm. I did not purge the air from the fuel line.
Joe Gores
 
My primary concern isn't that the Dynon and the mechanical gauge show different values, but rather why is my prerssure dropping 2 PSI as I increase the RPM's ? I called Van's yesterday and they suggested I call Lockwood.

I spoke with their support and they confirmed that falling pressure is not normal. However, the Rotax limits are 2.2 -8 PSI. Since I am above that, my pump is still considered ok. They suggested I fill out a service report so my issue is on record. If there are further issues I may still be covered by the warranty. He also suggested I disconnect the fuel line at the gascolator and run the engine off a remote fuel source aka, a gas can.

As far as air in the sensor hose, I am not sure if it has an effect or not. The last time I had low pressure, I "solved it" by disconnecting the hose, double checking that I had the restrictor correct, and putting everything back together. It worked fine for 20 hours.
 
Mark,
It seems that most RV-12 owners with fuel problems solve them by replacing the engine driven fuel pump. Have you monitored the fuel pressure with the engine running and the electric pump off?
Joe Gores
 
I have been in contact with Lockwood regarding the pump, and Dynon re: the fuel pressure readings on the Dynon. Both have been very helpful. Dynon tech support gave me the resitance values for the sender. At 0 psi it should read 11 ohms. At 5 psi it is 42.3. They indicated it should be linear in between.

My sender only reads 2.9 ohms with no pressure. They said it is defective and they are sending me one tomorrow. I felt there service was excellent. They are testing a 0-15 psi sender to replace the current 0-30. They don'tknow when it will be available. I offered to beta test for them, but the tech said they arn't there yet.
 
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