What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

EI FT-60 RedCube Reading Way Off After Fuel Pump Change

ssokol

Well Known Member
Sponsor
Replaced the mechanical fuel pump due to increasing fuel pressure drop-outs. Before the change the Red Cube fuel flow meter was dead on. After the change it is consistently reading high at all mixtures.

Normal takeoff WOT flow was in the 14 GPH range. It now reads 25 GPH.

Normal leaned for cruise at 75% power was 8 GPH. It now reads 15 GPH.

It is NOT a fuel leak. Several test flights including a long XC indicate that the engine's burn rate has not changed. It's not a software issue - I read the raw pulse count and did the math myself and the reading is much higher than it used to be.

FWIW: The engine is fuel injected. The cube is located at the bottom of the firewall in the correct orientation. It has worked properly for the past 90+ hours.

Any guesses? Bubbles? Cavitation? Gremlins?

Thanks,

-S
 
Replaced the mechanical fuel pump due to increasing fuel pressure drop-outs. Before the change the Red Cube fuel flow meter was dead on. After the change it is consistently reading high at all mixtures.

Normal takeoff WOT flow was in the 14 GPH range. It now reads 25 GPH.

Normal leaned for cruise at 75% power was 8 GPH. It now reads 15 GPH.

It is NOT a fuel leak. Several test flights including a long XC indicate that the engine's burn rate has not changed. It's not a software issue - I read the raw pulse count and did the math myself and the reading is much higher than it used to be.

FWIW: The engine is fuel injected. The cube is located at the bottom of the firewall in the correct orientation. It has worked properly for the past 90+ hours.

Any guesses? Bubbles? Cavitation? Gremlins?

Thanks,

-S
The fact that it is reading exactly 1.9 times high in both high and low flow rates points to consistency. When these fail, they seem to be very intermittent and bounce around between accurate and erroneous or go to zero outright. Never heard of one reading an exact amount high at all times. I can't see how air bubbles could cause a failure this consistent. My first guess would be a software, beyond that I am at a loss. They send square wave voltage pulses, so don't see how wiring can be a culprit. Intermittent voltage or ground issues wouldn't be this consistent.

Larry
 
Last edited:
A loose wire under vibration will cause a "make and break" connection that looks just like a pulse, and will be counted as a pulse. I had one crimped connection fail on mine early on with that result, my output was sometimes good and sometimes crazy high, depending on how well that broken connection was working. I've never seen one give a CONSISTENT reading like that though, I could watch mine go up and down in flight under stable engine conditions.
 
Thoughts From EI

So after checking the code, and the wiring, and the code again I finally did what I probably should have done in the first place and emailed EI to see if they had any thoughts. Here's their response:

Thank you for your e-mail. Anytime a part of the fuel system is replaced, it is not uncommon for the k-factor to require an adjustment. As long as the FT-60 is outputting a solid frequency, it is functioning. Typically, a small adjustment to the k-factor (if the monitor is equipped) should bring the fuel burn back inline. However, as you are now seeing almost double, the solution may be a bit more complicated. Is the 15.2GPH indication you are seeing solid or erratic? If it's erratic, there may be an air bubble trapped in the FT-60 that is refracting the optical beam, causing additional pulses. Is the FT-60 installed between two pumps? If so, it should be moved to where it is installed after any and all pumps. If it is currently installed between two pumps, the new engine driven pump may be cycling at a different rate than the previous pump, causing a "hammer effect", similar to what is heard in plumbing. This "hammer effect" causes the transducer's impeller to vibrate forward and backward quickly, creating additional pulses.​

The data is not at all erratic - it's very consistent. That tends to indicate that the problem is the "hammer effect" they describe rather than a bubble in the transducer housing. I'm going to have to pull the cowl off and check to see if the FT-60 is installed between the boost pump and the engine-driven pump or if it's after the engine-driven pump. My guess, based on the behavior, is that it's between them. If that's the case I'll re-plumb as directed and see if that fixes the issue.
 
... I'm going to have to pull the cowl off and check to see if the FT-60 is installed between the boost pump and the engine-driven pump or if it's after the engine-driven pump. My guess, based on the behavior, is that it's between them. If that's the case I'll re-plumb as directed and see if that fixes the issue.
Hey Steve, sounds like you are not the builder. I'm sure you know this, but anyway, please take care in making changes in this area. Small changes here using a non-standard method can cause big problems. There was a recent thread where a builder had an additional fitting after the mechanical fuel pump which came loose due to leverage on the fitting, and he sadly destroyed his aircraft after the engine quit and he landed in a field. Lots of good ways to re-plumb the red cube, and probably more bad ones, and the difference is not always obvious. There are several threads on this on VAF. Good luck!
 
Excellent advice - I'm good with bits and decent with electrons but a total novice with internal combustion engines. I have an A&P friend who does all of the FWF work with / for me. He changed out the fuel pump and if it turns out the red cube needs to be relocated, he will be the one doing the plumbing.
 
Excellent advice - I'm good with bits and decent with electrons but a total novice with internal combustion engines. I have an A&P friend who does all of the FWF work with / for me. He changed out the fuel pump and if it turns out the red cube needs to be relocated, he will be the one doing the plumbing.

The red cube install instructions are good, and if followed seem to eliminate such problems.

Here is how I mounted it in the current RV-8 - this placement satisfies the install requirements.
78-C6-A43-E-0-E36-43-DB-B5-F1-F4-D0-FCD3846-A.jpg


Carl
 
Back
Top