I just installed a few telemetry sensors, including a GPS-II, in my 40% aerobatic plane, which uses a Futaba radio and a PowerBox Competition SRS. As a quick background, the GPS-II and the transmitter, a Futaba 18MZ-WC, were recently obtained from another pilot, who previously used a PowerBox Royal directly connected to the GPS-II. In my plane, because it uses a Competition SRS, I had to connect the GPS-II as a regular Futaba sensor, connected to the SBUS-2 of the primary receiver (a R7003-SB). For that reason, I used the Terminal program to set the GPS-II to SBUS-2 mode of operation.
The PowerBox and the GPS-II (as GPS-1675) were already listed (registered?) in the 18MZ, when I set up telemetry in my plane. Now the Temperature sensor and the magnetic RPM sensor (both Futaba components, assigned to their default slots) work normally and provide credible telemetry data. The PowerBox (connected via the Teleconverter to the SBUS-2) also provides good data, starting at slot 8, in the first 8 slots (voltage and capacity of the two flight batteries, and radio performance parameters), and empty values in the next four slots, possibly associated to a connected GPS. However, the GPS-II , set to start at slot 24, gives out data totally inaccurate (for example, 15,000 ft altitude and only 97 yard distance after a 10 minute flight).
By the way, the GPS-II seems to be able to lock on the satellites, as indicated by its green LED which becomes steady after a short period of blinking.
What, if any, additional or different steps do I need to take, to make the GPS-II work correctly in my environment?