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  #1  
Old 11-20-2012, 11:01 AM
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ScottSchmidt ScottSchmidt is offline
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Join Date: Dec 2005
Location: Salt Lake City, Utah
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Default Fuel Pressure on start-up issue

Need some brains to help me better understand an issue we are having during the start-up.
Today, during the start-up, we were unable to see fuel pressure from the electric fuel pump. Before starting the engine the checklist says to turn on master and check for fuel pressure but there was no fuel pressure.
At first you would say it was a bad electric fuel pump. We shut everything down and checked the flow rate from the gascolator with and without the fuel pump on and it definitely is creating pressure but didn't know how much.
We then started the engine and fuel pressure came right up to 4-5 psi.
We shut down the engine for a few minutes, then turned the Dynon screen on and checked that fuel pressure was 0 psi. Then turned the master on (fuel pump comes on too) and the fuel pressure came up to above 2psi just as it should.
Has this happened to any of you?

So, why would it work after we started the engine but not before.

The plane has about 20 hours on it.
It has the new Dynon fuel pressure sensor installed.

Questions:
Could sitting for a week cause the fuel to run out of the line and the 2 psi from the electric fuel pump not enough to prime the system?

Is there a position on the mechanical fuel pump that would not allow the fuel to flow past it?
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Scott Schmidt
Salt Lake City, UT

RV-10 N104XP (1280 Hours)
RV-12 N321UT (Sold)

Last edited by ScottSchmidt : 11-20-2012 at 12:45 PM.
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  #2  
Old 11-20-2012, 12:22 PM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,678
Default Hey Scott - -

The fuel pump has flutter/check valves inside. Position of the mechanical pump plunger makes no difference. If the check valves were sticky they might not allow flow. 2 PSI seems to be enough to force past the check valves inside the mechanical pump, so maybe give it some more time. If no leaks, I don't see a problem. ( I know, easy for me to say).

John Bender
477.3 hours as of yesterday.
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  #3  
Old 11-20-2012, 01:55 PM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,234
Default

Quote:
Could sitting for a week cause the fuel to run out of the line and the 2 psi from the electric fuel pump not enough to prime the system?
No, the fuel system does not need to be primed after sitting for a week. After the electric pump runs for a few seconds, the fuel system should be pressurized. It does not matter if the fuel hose going to the pressure sensor is full of fuel or air. Air in the fuel line will be at the same pressure as the fuel. It is impossible for air in the line to be at less pressure than the fuel. If it were, then the fuel would flow until the pressures were equal. The sensor does not care what type of media is applying pressure to its diaphragm (as long as it is chemically compatible).
Make sure that all electrical connections and crimps are tight. Just because the sensor is new does not mean that there is nothing wrong with it. 2 psi seems on the low side. Engine vibration can help an analog instrument read more accurately by un-sticking the needle. The same principle might apply to a pressure sensor.
Joe Gores
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  #4  
Old 11-20-2012, 04:48 PM
RLH RLH is offline
 
Join Date: Jul 2012
Location: Orland Park, IL
Posts: 4
Default I forgot where the actual sensor is!

I have a similar problem. Last week I noticed that the fuel pressure was reading a little low on take off. This week, there is no fuel pressure reading at all - just a red "X" accross the bar on the EMS!

I have forgotten; where is the actual fuel sensor? Is this part of the electric fuel pump, (which will be a real pain to change) or is it a separate unit?
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  #5  
Old 11-20-2012, 08:27 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
Posts: 3,161
Default

Follow the fuel line back from the pressure regulating stack. The sensor should be on the firewall if you didn't deviate from the plans.
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  #6  
Old 11-21-2012, 10:17 PM
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ScottSchmidt ScottSchmidt is offline
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Default UPDATE

I did find the cause of the issue but have another question.
Tonight I went to the hangar and checked to see if the electric pump would show fuel pressure and sure enough it did which makes it hard to find the problem.
Dynon confirmed that if the electrical connection was not working it would show a red X on the screen.
So I started checking flow in the lines to see if there was anything plugging a line.
I started at the manifold bolt on the top where the fuel flows to the sensor and the return line back to the tank. It looked fine.
Next I pulled off the fitting at the fuel pressure sensor and an orange-ish colored gel came out.
I removed the fuel pressure sensor completely and cleaned it out. Here is a picture I took with my iPhone that shows some of this gel like substance in the pressure sensor.


Now the events from last Tuesday make more sense. It was an early morning flight. The plane had been sitting in the cold hangar which most likely caused this gel to harden to the point where the electric fuel pump would not allow the sensor to see the pressure. Once the plane started, the additional pressure from the mechanical fuel pump pushed the gel to the sensor. Then after shutting down the gel had been moved or dissolved enough to see the pressure from the electric pump only.
It has been warmer (in the 50's) the past few days which is most likely why we could not replicate it.
Now the question is where did this gel come from and will it come back?
We are burning auto gas with ethanol in it. Has anyone seen this or have an idea where it comes from?
I plan on checking every 10 - 20 hours to see if it returns.
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Salt Lake City, UT

RV-10 N104XP (1280 Hours)
RV-12 N321UT (Sold)
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  #7  
Old 11-22-2012, 07:20 AM
JBPILOT JBPILOT is offline
 
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Location: Jesup, Iowa
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Default Hey Scott - -

Another thing you might want to check. FIRST - did you use Locktite on the fuel line fittings ? A few years ago, I used Locktite on another plane I built, and after a few early flights, the engine nearly died in the air. Finally found out a perfectly formed small ball of what looks like the same stuff had formed in the carb bowl, and was just big enough to plug the main jet. When I took it out, it was fairly firm. All I could figure was that it slowly accumulated in the bowl, and formed into a small ball.

Bottom line, you might want to pull the bowls of the carbs and see if any is in there also.

John Bender
477.3 hours
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  #8  
Old 11-22-2012, 10:09 AM
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ScottSchmidt ScottSchmidt is offline
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Default No loctite

I did use a little of the EZ Turn but tried very hard to keep it away from the first 2-3 threads. This did not appear to be that.
We can pull the float bowls and check, that is a good thought.
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Salt Lake City, UT

RV-10 N104XP (1280 Hours)
RV-12 N321UT (Sold)
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  #9  
Old 11-22-2012, 12:12 PM
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Tony_T Tony_T is offline
 
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Location: Lacey, WA
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Default Orange goo

I too found orange colored goo in the sensor line at one point in time. I have no idea what caused it, but the plane wasn't old enough to have fuel go bad in the line even though I use auto fuel with ethanol.

The only contaminant I can imagine would be the fire sleeve dip that the ends of the fire sleeve are treated with when the fuel lines are fabricated. I think it would be possible for some of it to get into the braided fuel lines if the fire sleeve was pushed on before the dip set up. Just a wild guess on my part with no evidence other than the suspicious color.

I found no contaminants of any kind in my float bowls at the annual inspection. If there was any of this stuff in the fuel lines that were actively flowing fuel it went through the engine.

I do know of one other RV-12 that had the same stuff in the fuel sensor line and I believe he was using Mogas without ethanol.

Tony
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E-LSA RV-12 ULS
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  #10  
Old 11-22-2012, 01:41 PM
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ScottSchmidt ScottSchmidt is offline
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Default Interesting....at least 3 now.

Quote:
Originally Posted by Tony_T View Post
I too found orange colored goo in the sensor line at one point in time. I have no idea what caused it, but the plane wasn't old enough to have fuel go bad in the line even though I use auto fuel with ethanol.

The only contaminant I can imagine would be the fire sleeve dip that the ends of the fire sleeve are treated with when the fuel lines are fabricated. I think it would be possible for some of it to get into the braided fuel lines if the fire sleeve was pushed on before the dip set up. Just a wild guess on my part with no evidence other than the suspicious color.

I found no contaminants of any kind in my float bowls at the annual inspection. If there was any of this stuff in the fuel lines that were actively flowing fuel it went through the engine.

I do know of one other RV-12 that had the same stuff in the fuel sensor line and I believe he was using Mogas without ethanol.

Tony
That is interesting. I blew every line out with an air hose so I know there was nothing big in the lines but you may be right.
It would be interesting to have someone who is having low or high fuel pressure readings take this connection apart to see if they have the same thing.

I am about to start the annual on the -10 and plan on checking that location as well.
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Salt Lake City, UT

RV-10 N104XP (1280 Hours)
RV-12 N321UT (Sold)
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