tacho needle interference

[pen15]

hey all in my trip to japan i found myself a defi tacho installed sweet now the problem i face is this when under heavy load at around 5000 rpm the needle starts to jump up and around 9000 rpm now i think this is interference with something now this is what i have thaught about

-stock guage is still wired up interference from that?

-coil playing silly

-dizzy playing silly

-aftermarket ecu givving funky readings or signal to coil

now does anyone know of a line filter i can hook up to smooth out the interference

thanks all
mat

[pen15]

so nobody knows of an inline filter to go between my gauge and my coil?

[tuned86]

I'm bit rusty with this but you could try 100ohm and 100nF ceramic cap and increase/decrease accordingly. Otherwise use a RC filter calculator for more accurate

30-400Hz range is what you are working with for rpm.