My "firmware " software has the "#define RPM_sensor_ line_Input 1 line. I did not change it.
I checked with the Arduino site and see that the Micro interrupt 1 is indeed connected to D03, so that was a blunder on my part.
Since Allan is seeing signals at the input pin, and did not have the problems Phil had with compiling, and since Phil´s project is working, I would suspect that Allan has a problem with the interrupt handling. I would recommend that Phil provide Allan with information regarding versions/sources of the the Adafruit/Arduino libraries he used for his compilation.
Good luck and best regards,