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  #21  
Old 08-01-2017, 05:24 PM
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JonJay JonJay is offline
 
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Have you pulled your EMS data and looked at your fuel pressure coinciding with the known event?
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  #22  
Old 08-01-2017, 07:48 PM
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vernon smith vernon smith is offline
 
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Location: Naples FL
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I'm a neophyte to aviation systems but these type of problems are solved with header tanks or swirl pots in other applications. Some added weight and plumbing complication, maybe six pounds including the tank/pot and plumbing.
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  #23  
Old 08-02-2017, 08:21 AM
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Guy Prevost Guy Prevost is offline
 
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My RV-10 has Bendix mechanical fuel injection, so this may be useless information.

I had a similar issue that was resolved by one (or both) of two changes. I moved my fuel flow transducer from the tunnel where it was on the suction side of the system to the pressure side of the system between the servo and spider. I did this because having it on the suction side invites vapor formation at the transducer, especially when heat soaked. While performing this work, I did find evidence of a slight leak at the outlet of the electric boost pump. I could never smell fuel--I just found a little bit of staining at the fittings. I had no more issues after those two corrections.

Best,
Guy
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  #24  
Old 08-02-2017, 09:04 AM
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Bluelabel Bluelabel is offline
 
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Thanks for all the input... even though I just got done my condition inspection and had the tunnel open, maybe there is a chance of a leak that will invite air yet not leak any fuel. Time to put a wrench on each fitting again.
I will also see if running both pumps at the same time helps.(the problem is the the situation happens so infrequently).
I can pull my Garmin data logs. I'll should be able to at least see the conditions of flight.
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  #25  
Old 08-05-2017, 06:25 PM
Strasnuts Strasnuts is offline
 
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+1 for Jonjay and Jesse.

I've never experienced a hiccup in the 800+ hours of switching. I have a stock setup engine with an andair fuel valve.
I don't use the electric pump in the process.
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Last edited by Strasnuts : 08-08-2017 at 06:50 AM. Reason: added info
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  #26  
Old 08-05-2017, 07:11 PM
nilberg nilberg is offline
 
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Location: Katy, TX
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Here is my theory:
I assume your valve is above the tank fuel level. The fuel line is also in suction upstream the electric pump. I think you have a small leak in the line, probably at the valve connection. When sucking fuel, there is no fuel leak, just air suction, so small that the engine is ok with it. When the fuel line is inactive, the small leak is causing air to be sucked in causing venting and leveling with tank level. Now you have a air pocket in the line and next time you switch over, the engine stumbles.

Last edited by nilberg : 08-06-2017 at 09:40 AM. Reason: Misspelling from autocorrect
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  #27  
Old 08-06-2017, 07:34 AM
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David-aviator David-aviator is offline
 
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What does Robert have say about it?
He must have an explanation, it's his system.
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  #28  
Old 08-20-2017, 04:35 AM
amekler amekler is offline
 
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Location: Gilford,NH
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i've had this happen twice in my 8 years with n668g
both were on hot days running lean of peak and changing tanks without using the boost pump. i've never had it if happen when using the boost pump.
Alan
n668g
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  #29  
Old 08-20-2017, 11:15 AM
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Bluelabel Bluelabel is offline
 
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Quote:
Originally Posted by David-aviator View Post
What does Robert have say about it?
He must have an explanation, it's his system.
We talked and he doesn't have an answer as I need to have more info about the facts when it happens... I flew last week, it was hot climbing out of Bakersfield, Ca. Hit both pumps before switching tanks and didn't have an issue.
EFIS data also doesn't show anything. For some reason, the one thing not shown on my EFIS data when loaded to Savvy is Fuel pressure. I went back and looked at a flight coming out of Arizona, where I know when it happened, and could not find any data irregularities.

I can say, that I think it only happens when hot and high. I have started using both tanks for equal time on the ground to prevent any hot fuel from sitting in one side.
I'll see if it ever happens again, and note all the facts.
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RV-10 N265WD
"Miss Whiskey Delta"
BPE IO-540, FULL EFII
KMYF, San Diego, Ca.
KEOS, Neosho, MO

Crew Lead on the
Grove Aero Super Legacy Reno Racer,
twin turbo, IO-540,
full EFII management system
!

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  #30  
Old 08-20-2017, 02:45 PM
n816kc n816kc is offline
 
Join Date: Jan 2005
Location: Winter Haven, FL
Posts: 198
Default fuel return

Hey John,

I've had a similar issue with my -6 , fingers crossed we got it figured out last week when doing the condition inspection. Somewhat different symptoms, but it may give you some insight.

I've had an intermittent issue when switching to the right tank - air was entering the fuel lines and the AFP injection system would react with a rise in rpm and fuel flow, followed almost immediately by cutting out/stumble when the air made it to the injectors. I did the tighten all the b-nuts, check the vents and look for fuel staining thing with no relief. I thought for sure it was a leak at the Andair valve letting air in on the right tank line (fuel selector is the high point in the system before the pump). But again, no fuel smell or stain to help diagnose.

At shut down before starting the compression checks this year, I had an a-ha moment when I heard the vapor pushing fuel past the injectors. The fuel return line is in the plenum also, and subject to the same heat/vaporization - could it be pushing fuel all the way through to the line and putting vapor in the system?

The only difference between the right and left side fuel systems in my plane is the fuel return from the injection system (AFP with purge valve installed). The fuel return is T'd into the supply side line on the right. The T fitting is below the mid-tank level and fuel level in the tank has never made a difference in the occurrence of the issue. I didn't consider that air could enter the fuel flow there since the fuel supply line is lower, and fuel level higher, than the T. I also didn't consider the volume of vapor that could be produced in the return line back to the supply line.

Only one way to find out. We capped the T in the supply line and plumbed the fuel return into the vent line. Checked on the ground with the electric pump only, didn't push any fuel out the vent, but it did go right into the tank as expected. Run up checks all good with normal operation.

Five flights later, with both cold and hot starts, I haven't had an issue when switching to the right tank. Like I said, fingers crossed, but I think we've got it figured out.

Long story short, if you have a fuel return line from the injection system, check how it's plumbed.
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