When input is from petrol engine, Actisense EMU-1 tachometer input must be connected to alternator (not ignition coils)
Article HD25033, May 26, 2015
Actisense EMU-1 (firmware verfsion v0.070), when connected to a petrol engine, needs the tach inputs originating at the alternator.
When an Actisense EMU-1 is connected to the ignition coils of a petrol engine, there is more "ringing" in the signal which make analysis of true RPM frequency more difficult. This issue does has little bearing on diesel engines however.
Do not connect the EMU-1 to the ignition coils of a petrol engine. Connect to the alternator for tachometer readings; this should supply a clean signal and accurate conversion to digital NMEA 2000 data.
Future versions of EMU-1 calibration software and the EMU-1 firmware may rectify this issue.