RED CUBE fuel flow calibration number?

[BMW_X6M]

I am wondering what calibration number users have found to be the most accurate. I have been trying to get this right, and have bounced around going up and down. I would like to start with full tanks, fly, and then have the fuel used equal what I end up refilling with. Right now I am using a calibration number of 72000. I think I need to go up from there. The refill amount right now is about 1 gallon less than the calculated fuel used.
Any insights would be welcomed. Thanks.

 

[preid]

There is a calculation for this in the latest installation manual page 7-56. I did one calibration and it is within .4 or less each time. It used to be within .2 when I actually inputted the fuel added versus just saying it "full" now- when it may actually be .1 lower on each side.
In other words the instructions in the manual work!

I did two fillups and that was plenty to get it close enough.

 

[65xx]

I go the other way, my Red Cube number is 65,000 and still closing in on the "perfect" number. Dan

 

[dynonsupport]

So, if you're just bumping the number up and down, try using the prescription in the manual, which takes the fuel computer-observed number, against what you fill up with, to obtain a correction factor.

 

[BMW_X6M]

OK, I think I did the calculation wrong when I did it the one time, and ended up with a strange correction factor, that threw me way off. I will start over, and log several fill-ups, and then make the correction factor calculation.

Does the fuel line routing with bends before or after the sensor make a difference? I am a carburated engine by the way, so this is low pressure fuel. Is there a difference in accuracy between high or low pressure fuel? Thanks!!!

 

[preid]

there are rumors that if the cube is between the electronic and engine fuel pump that the number gets boosted when the electronic is on.. but that should not be much. As mentioned above less than .4- but that is to your advantage- it means you actually have up to .4 MORE fuel than it shows.
Do one fill up and change your number to match closer to what you fill up. Than fill up again and go from there.

 

[mmarien]

Check page 7-41 of the Installation Manual for recommendations for installation of the red cube fuel flow sensor. It recommends against 90 degree fittings on the fuel flow sensor to avoid turbulence but the fuel line will need bends and elbows in the normal installation. You also don't want to capture air pockets in the cube so the line leaving the cube should have an upward slope away from the cube so any air can escape.

I had the phenomena of the fuel flow increasing for a moment when I turned on my electric fuel pump upstream from the cube, but it only lasted until the pressure stopped rising. The flow was increased as more fuel is needed in the line to increase the pressure. If the engine wasn't running, the flow would fall back to zero when the pressure stabilized or maximized. With the engine running there was no increase in the fuel burn just because there was more pressure in the fuel line. And eventually when the electric pump was turned off, the flow would slow down as the pressure decreased. So really there was no increase in volume, just an change in rate for a moment. In the end I believe it didn't make a difference in the volume as the increase in flow was canceled by the decrease in flow when the pump was turned off.

 

[BMW_X6M]

UPDATE: My fuel used number is now very close to the amount I need to add to fill the tanks back up. I followed the instructions, and arrived at a corrected number. Right now the old number was 75,000 and on the last tank fill was less than a 1/2 gallon off. I did another calculation and the new number is a little over 76,000.