@Tan The Fuel Gallons (GPH) comes from the JPI Fuel Transducer, I don't believe it has anything to do with any inputs from the GPS.
My shop tried several iterations on JPI and GPS and in now works for me. Here is what I have that works:
- JPI - GPS Format: #6: GNS 430/530-WP
- Garmin GNX-375 - RS-232 Interfaces:
- Port 2: Aviation Output 1 (for the JPI)
BTW - on the ground, 3 of the side channels on the JPI were X'ed out: 1- H:M, 2 - REQ, and 3 -RES. EXCEPT - on my GNX-375 there is the initial test mode on Power Up, first it confirms Databases (I press Continue), then it goes into a mode to confirm the CDI gauge - in my case i have a G5 DG/HSI, so I can verify the indicator shows what the GPS has. At this point, these 3 X'ed out JPI channels display info and let you know the GPS and JPI are talking on these channels. Once I press Continue again to leave test mode, the JPI then X'es out those 3 channels again.
The 3 X'ed out channels require the plane to be in motion to calculate Time to Waypoint - assume it get GPH (from JPI fuel flow transducer) and Time to waypoint (from GPS) to calculate, If the Time part is Zero - dividing by 0 gives Infinity, so the JPI just X'es out as it can't calculate what to display. Once airborne, the GPS calculates a Time to Waypoint and these 3 Channels come alive on the jPI.
Let us know if you can get yours to work