GI 275 EIS Fuel Flow Issue - Resolved

[CCAS]

Troubleshooting a new GI 275 EIS install issue and could use recommendations.  Aircraft is an M20J with IO-360 A3B6D engine with GEA-24 interface. 

On the first flight after avionics upgrade I found the fuel flow on the new GI 275 EIS was reading about double what it should be (e.g., approx 35 gph on takeoff/climb and about 20 gph at 65% power in cruise (leaned +25 ROP) at 8500' MSL).  I brought the airplane back to the avionics shop to investigate.  They're asking me on the next flight to perform the Fuel Flow Recalibration procedure found in the GI 275 pilot guide (190-02246-01 Rev S on pages 97 & 98).  When I read that procedure, it appears to modify displayed fuel flow based solely on applying a percentage correction to the EIS's last calculated fuel consumption data against actual pilot-entered fuel used.  Why wouldn't the newly-installed Fuel Flow Transducer be providing accurate independent FF data to start with?  Could the wrong transducer have been installed (or maybe the correct transducer was installed in the wrong location)?  I'll ask tomorrow  what K-Factor the shop used during the EIS configuration but I would have thought that'd be the first thing they'd check.         

Edited June 26 by CCAS
Problem is resolved

[jetdriven]

The Pilot adjustment will only do a 10 or 15% adjustment. It sounds like they won't have the wrong K-factor. Have them use the table 5-26 to select the right FF transducer.  if they cant find it, double the K-factor you have to start. 

Edited June 22 by jetdriven

[CCAS]

4 minutes ago, jetdriven said:

The Pilot adjustment will only do a 10 or 15% adjustment.

Thanks Byron!  That's good info.  I'll point them toward Table 5-26 and see what K factor they end up with.   

[rklems]

Agree with @jetdriven they have the wrong k-factor.... Do you know what fuel flow transducer was installed? Sounds like it was new with this EIS install, so they should have had the proper data. If they interfaced it to a factory fuel flow transducer, I believe those are Floscan units.

[testwest]

If it is possible look at the FloScan and see if there is a number written on it, that should correspond to the calibrated K-factor of the unit. They are all a little different. Or, look for and find the tag from the unit. In the example below the "16-3492" number means the transducer factory-calibrated to a K-factor of 34,920, that is the number of pulses per gallon at 16 gph fuel flow (gasoline).

More great info here: 

https://floscaninc.com/specifications/

From the table at the above location, the "approximate" K-factor for this 201A-6 is 32,000, but it was actually measured at 34,920. You will save a lot of iteration by having the mechanic put in the exact correct K-factor to begin with. Or better yet, do it yourself!

 

[CCAS]

On 6/23/2025 at 12:54 AM, rklems said:

Do you know what fuel flow transducer was installed?

The shop confirmed they installed the FT-60 FF transducer that came with the Garmin EIS installation kit.  However, they also said that in the EIS configuration pages, the FT-60 can be identified as either an "FT-60" or by the specific Garmin part number; prior to my first flight, they configured it as the Garmin part number (not as an FT-60) with a K Factor of 68000.  They've now re-configured it as an FT-60 with a K Factor of 68000 and I'll fly it again tomorrow to see if it makes a difference.    

[CCAS]

12 hours ago, testwest said:

If it is possible look at the FloScan

The shop confirmed they installed an FT-60, not a FloScan but I appreciate the thoughts and comments.  I did find it interesting that when the shop first contacted Garmin about the issue last Friday, the tech support folks recommended changing the K Factor as a first step (I think they recommended something like trying 29000 pulses per gallon)....but I think that would have made the fuel flow indication double instead of half'ing.  So we're going to try again tomorrow with 68000 set after re-configuring the FF as an "FT-60".  I should know more tomorrow. 

Thanks again.  

[CCAS]

Closing this topic out after resolution today. 

The solution ended up being pretty simple.  The problem was indeed an inadvertent K Factor issue caused by a setup oversight.  The default K Factor on the FF transducer configuration page is 29000 pulses per gallon. The installation manual calls for the K Factor to be 68000 ppg for the FT-60 so the installer has to update that field.  However, after changing the K Factor value to 68000 and selecting "Enter" you have to wait 5 seconds or so for a small green square in the top right corner of the display to appear and then start blinking.  After it blinks 3 times it then turn into a check-mark.  If you navigate away from the setup page before the check-mark appears, the system will switch the K Factor value back to the default value without you knowing it. 

EIS is working great now! 

 

[rklems]

Ah yeah, the GI 275 <-> GEA sync has gotten me a few times too... seems like they should give a better indication that a sync is occurring and to wait for that to complete. There are a few places in the UI that it puts up an overlay with some animated ... when it's doing the sync, but it doesn't seem to be consistently applied everywhere there is a sync that needs to occur.