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  #11  
Old 07-05-2022, 08:39 PM
VA Maule VA Maule is offline
 
Join Date: Apr 2016
Location: Bucking ham, Virginia
Posts: 289
Default Red cube

Per the instructions that came the red cubes (I have 2 one for the return to tank) ďthe wires exiting the cube body must point up !Ē Yours is 90* off going directly through the firewall and the little counting wheel is laying flat instead of being vertical.
Iíam suspecting whatís happening is with the boost pump off the cube is in a vacuum situation as the mechanical pump is drawing fuel through the pump, when everything including the fuel gets hot forward of the firewall some fuel vapors form and hang out in the top of the wheel chamber of the cube and fail to make the counter wheel spin consistently and the incorrect orientation compounds the problem. When the boost pump is turned on the red cubeís situation changes to being a pressurized condition and fuel flow can exert enough pressure to make the counter wheel spin appropriately.
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  #12  
Old 07-05-2022, 09:28 PM
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MacCool MacCool is offline
 
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Location: central Minnesota
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I apologize for mislabeling the title of this thread. It says feel flow, but the actual variations and fluctuations are in fuel pressure and I was unable to go back and change the thread title. The red cube itself appears to be working just fine. Over the last several weeks, my fuel computer showing indicated ďgallons usedĒ matches the pump gallons within 1/10th of a gallon using the default K factor of 680. The previous red cube likewise worked great in that location until it went TU recently after 10 years and I replaced it. Displayed fuel pressure however does demonstrate fluctuations when the engine is hot. I do think itís heat related, and I am going to put a heat shield on that exhaust as well as insulate the fuel lines. I really appreciate everybodyís help and interest and I apologize for screwing up the title.
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RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff

Last edited by MacCool : 07-05-2022 at 09:34 PM.
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  #13  
Old 07-05-2022, 09:48 PM
VA Maule VA Maule is offline
 
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Location: Bucking ham, Virginia
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Where in your system is the pressure sending unit ? The red cube only reads flow it has absolutely nothing to do with pressure. Relationship of pressure sender position in the fuel lines configuration could have the same issue with being in a vacuum/suction versus pressurized condition.
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  #14  
Old 07-06-2022, 04:49 AM
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MacCool MacCool is offline
 
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Pressure senders and oil temp sit on the firewall toward the top.

Thereís a service bulletin from Advanced Flight on those oil and fuel pressure sensors. I have the new Kavlico sensors but havenít installed them while I wait to get this particular problem sorted out.
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RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff

Last edited by MacCool : 07-06-2022 at 07:49 AM.
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  #15  
Old 07-06-2022, 05:00 AM
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MacCool MacCool is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
Mac,

I suggest you have some basic issues that need to be fixed before you go chasing possible fuel line heat causing your pressure drop.

Looking at the photo, I note that you have the fuel line going into the (new) red cube, then into your electric boost pump, then I assume to your mechanical fuel pump. I also note a bunch of 90 degree fittings.

I refer you to the EMS install instructions on placement of the red cube (as in between the engine driven fuel pump and the engine and not mounted on the engine) and fuel line considerations on the input and output of the cube.

Carl
Thanks Carl. I’ll have to look at it again (I didn’t build it) but my recollection is that fuel goes from the
engine-driven fuel pump —> boost pump —> red cube —> engine. My understanding is that the firewall-forward was done by Don Swords at Don’s Dream Machines.
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RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff

Last edited by MacCool : 07-06-2022 at 05:08 AM.
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  #16  
Old 07-06-2022, 05:54 AM
Majorpayne317641 Majorpayne317641 is offline
 
Join Date: Sep 2021
Location: Goldsboro, NC
Posts: 86
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The way mine is built, the boost pump is inside, from the feed tanks to the electric fuel pump, mechanical fuel pump, throttle, red cube, divinding block, cylinders. Never had any issues with that set up.

Last edited by Majorpayne317641 : 07-06-2022 at 05:57 AM.
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  #17  
Old 07-06-2022, 06:20 AM
Southern Pete Southern Pete is offline
 
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Location: England
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Do you know for sure the fuel pressure indications are accurate?
What is the min pressure required by the engine (from the book)?
You could always change the limits displayed on the EFIS.
I tend to agree with the others, fuel pump FWF and lost of 90 deg fittings could be your problem.
Can you fabricate a cooling shroud fed with cool air from the baffles to cover the pump and try to reduce temps?
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  #18  
Old 07-06-2022, 07:15 AM
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MacCool MacCool is offline
 
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Right now, the only actual problem Iím having with fuel pressure is a wonky fuel pressure gauge reading when the engine is hot, as well as some mildly hard starting. I see those fluctuations primarily on taxiing back after landing, although the engine runs fine. Itís not an issue on climb out after I turn off the boost pumpÖpressure readings solely on the engine driven pump at that point are rock steady and in the green.

I think that the fluctuating readings and hard starting when hot are likely attributable to fuel vapor in the lines and from what Iíve read here, Iím hopeful that some exhaust shielding and fuel line insulation will help with that. Thatís where I think Iíll start. The engine has run reliably for 500 tach hours with the current fuel configuration, about 250 of those hours in the Atlanta area. I did replace the Weldon boost pump at 450 hours due to a small leak, and the Red Cube at about the same time due to failure.
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RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff
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  #19  
Old 07-06-2022, 07:36 AM
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MacCool MacCool is offline
 
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Quote:
Originally Posted by Southern Pete View Post
Do you know for sure the fuel pressure indications are accurate?
What is the min pressure required by the engine (from the book)?
You could always change the limits displayed on the EFIS.
I tend to agree with the others, fuel pump FWF and lost of 90 deg fittings could be your problem.
Can you fabricate a cooling shroud fed with cool air from the baffles to cover the pump and try to reduce temps?
It’s a fuel-injected engine so needs higher fuel pressures…Lycoming wants 14 psi minimum, and taxiing while hot drops me down to 8 -12 psi on the gauge. I don’t know if the readings are accurate in an absolute sense, only that they are repeatably wonky/low at 900-1100 rpm when the engine is hot, repeatable rock-steady in the middle of the green when the engine is cold/cool.

Fuel line routing and configuration, and especially boost pump location, might be an issue, but it would be a PITA to re-configure and although I appreciate the input, I’m gonna put those fairly far down the list of things to try.
__________________
RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff

Last edited by MacCool : 07-06-2022 at 07:51 AM.
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  #20  
Old 07-06-2022, 10:52 AM
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Janekom Janekom is offline
 
Join Date: Jan 2006
Location: South Africa
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As an AP I would like to chime in here.

First of all I see a HUGE fire risk with the piece of soft aluminium tubing between the pump and the Red Cube. It is simply not good practice and should be taken out before further flight.

Then like others have mentioned.
1) Get rid of those 90 degree fittings. You just have to.
2) Make sure you use proper fuel lines and fire sleeve them.
3) I would install the electric boost pump and the red cube behind the firewall.
4) Install the Red Cube with the leads pointing up.
5) Make sure that there is a restrictor installed between the fitting on the engine pump and the line running to your FP sensor.

Questions:
1) Where is your main fuel filter installed?
2) What is your fuel line like from the red Cube onwards to the injection body and how is it routed?
3) What is your fuel line like and how is it routed from the injection body to the spider on top of the engine?
4) How is your system configured/plumbed?

One good example of the configuration is: Fuel selector - fuel filter - Boost pump - Red cube - engine pump - FI body - spider. there are also others.
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