If your RPM shows "dips" (sometimes jumping, usually to 0), use the latest firmware, at least
To understand more of the analog and rpm input, a schematic would really help.
- the RPM input is divided internally towards 5V, so about 0.6V on RPM input will be about 2.8V internally, equal the RPMref threshold.
- RPMref (often around 2.8V), can be changed with pulldown resistor to GND, or pullup to eg 4V