I see lots of talk about RF chokes, but that all seems to be in the Mhz range, where the big ignition pulses are all in 10s to 100s of Hz, and with pulsewidths more like those of a 40khz signal. I'm thinking about trying RC filters on all the cable lines, switching to proper twisted pair wiring, and/or TVS diodes.
Ignition pulse occur at 10s to 100s of Hz but, the signals produced by them are transients that cover many frequencies. If you could imagine a signal "blast" kinda of like hitting 30 piano keys all at once. It would sound like one bad note but, the note contains many frequencies both high and low Hz.