Solve the problem and bottle is headed your way!

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Good morning all,

I have a strange issue that has seemed to stump everyone (including me) that I have spoken with. If you can figure out this jigsaw problem of symptoms, a bottle of something pleasant to drink will be headed your way.

Background: Lancair IV-P, TSIO-550. Had an issue where even with the low boost on climbing through 16-17,000 ft the fuel flow would drop below spec (41-43) at WOT in the climb. Mentioned this as a squawk on condition inspection when it went to airframes a few months ago. No smoking gun found during condition inspection, no changes made to fuel system except that electric fuel pump (dukes) was found faulty and needed to be replaced.

Dukes pump was overhauled, and when I went to pick the airplane up, ground run of the engine went great. Here is where the fun starts. On departure from airframes, as is my normal habit pattern, as the fuel flow began to drop below 41gph, I turned the low boost on. I immediately experienced a drop in fuel flow (down to 34-35gph) and a corresponding rapid increase in all EGT's and CHT's. I turned the low boost pump off again, and the fuel flow returned to what it was previously in the climb.

There are several more funny and not so funny stories to be told about the testing over the last few weeks, but I will try to distill the information in to bullet points here to make it easier to digest.

Problem: When I turn the low boost pump on at WOT, i experience a rapid drop in fuel flow down to approx 35gph

Assumptions: The fuel system is physically connected correctly (looked at by airframes and the local engine shop), and at this point I assume the engine driven pump and electric pump are not defective.

Things that we know for certain or have been tested

  1. Fuel vent lines checked on both wing tanks
  2. Dukes pump overhauled (twice, last by CJ aviation here in miami and bench tested)
  3. Engine driven fuel pump replaced
  4. Full fuel system setup done per the SID (twice)
  5. Full power engine run on the ground with low boost pump on and off  (pressure within spec range)
  6. Pressure test on metered and unmetered side, with only electric fuel pump on reads correct output pressure of pump on high and low setting
  7. When i go to drain fuel from the gascolator, it will not drain, even though fuel is physically present in the gascolator
  8. gascolator checked for debris and none found
  9. Low boost pump turned on at low altitude (1,000 ft) and engine stayed at 41-43gph until approx 6-7,000 ft, then began to drop rapidly to 35gph...Turned low boost back off again and fuel flow returned to 41-43 and then began to decrease (as it normally would with low boost off in the climb)
  10. I have done all of these tests pressurized and unpressurized
  11. I have done all of these tests feeding from the left and the right tank
  12. I have tried, for testing to turn the high boost pump on in flight, and see an immediate rapid rise in fuel flow...I turned back off again approaching 50gph.
  13. On the ground, with the gascolator on, i have had the drain locked open and run the low boost pump....fuel comes out, as it should. I then close the drain, run the pump again for 6-9 seconds...and am unable to drain fuel from the gascolator, even though fuel is physically present inside it.
  14. I am able to prime the aircraft for starting effectively

Thank you in advance to the group!

Cheers,

Aaron

 

Aaron, I have the same engine

Aaron, I have the same engine as you in my LIV-P but don’t yet have a lot of experience with it. Had an IO-550-N in my Stallion so am familiar with fuel setup. Offhand it seems that your electric fuel pump is not vented adequately and this is why no flow from Gascolator even with gas inside. You might connect a plastic tube to the outlet of the fuel pump and run down vertically to simulate the Gascolator? Fill the vertical tube and then see if it will drain; don’t shake the tube to allow air to go up. If it doesn’t drain the fuel pump is suspect. My Stallion was a 6 pl. high wing with multiple causes for fuel starvation. I found that using clear tubing gave great feedback to actual happenings; e.g. proper venting. Don’t believe common thinking as to what should happen as It is commonly wrong. Good luck.

Tom

Aaron,

Aaron,

Thinking about this more seems like a venting issue which may restrict passage of fuel through your electric fuel pump in low boost. In point 13 above, where do you think the air that was in the Gascolator goes/went when the Gascolator is now filled with fuel? My guess is up the fuel chain where a suction is created. This same suction phenomenon may be the cause of the problem. Sonja Englert has a great book on troubleshooting engine problems. You might reach out to her.   caro-engineering.com   
Best,Tom

Has all of this been done

Has all of this been done with both left and right tank selected on the fuel selector?

Sure has

Sure has

artairman's picture

Onset with increasing

Onset with increasing altitude suggests an air leak into the system somewhere, thus inadvertently leaning the mixture (leading to the increased EGTs). Do you have any blues stains on the spider valve indicating a possible internal diaphragm rupture?

No blue stains......This

No blue stains......This problem happens immediately after selecting the aux pump to "low"

artairman's picture

I had to overhaul my throttle

I had to overhaul my throttle body/fuel controller and manifold as well as my engine driven fuel pump to resolve similar symptoms. Not sure how your inability to drain a full gascolator relates.  Good luck!

Conrad Huffstutler's picture

I would go after the vapor

I would go after the vapor vent return system.  The small line that comes off the top of the fuel pump that returns excess fuel to the corresponding fuel tank that is selected.  I have heard stories of interesting clogs in that system.  Also make sure your fuel vent check valves are installed the right direction and have a small orifice hole through them.

Is it ever difficult to remove a gas cap after a flight?  On the same idea, try selecting the RH tank and then remove the fuel cap while sumping the gascollator to see if there is a flow increase.

bknotts's picture

Just a thought--The issue is

Just a thought--The issue is raised at altitude.  This suggests it may have something to do with differential pressure.  The fuel in the lines in the cabin prior to the electric fuel pump are at external atmospheric pressure.  Combine that with the relative positive pressure in the cabin may allow air into the fuel system on the 'suction' side of the electric fuel pump but only when the differential air pressure is high enough.  My guess would be the fuel valve or the intake side of the electric fuel pump.  No leaks when there is no pressure in the cabin, then an air leak into the fuel line when pressurized.  A reasonable test would be to go to altitude unpressurized (of course, on oxygen) to see it the same thing happens.  I've never seen anything like that...like I said, just a thought. 

Hi all,

Hi all,

for the group the issue ended up being a clogged variable aneroid in the engine driven fuel pump.  This was after it had already been overhauled <5 hours ago.  
 

turns out you can’t rule out a component just because it is fresh out of overhaul 

 

thank you to the whole community for your help! 

1. Congrats! I've watched

1. Congrats! I've watched this thread with interest and it's great that you found the proverbial smoking gun.

2. Wait, some fuel pumps incorporate variable aneroids? I never knew that. While searching for more info, I came across an article that seems to describe the problem you encountered: http://www.kellyaerospace.com/articles/ContinuousFlow.pdf

3. Do you know what gunked up the pump? Just curious.

4. Congrats again!

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