Speeduino MPFI vs Holley Sniper EFI or MPFI vs TBI(my observations)

It is not necessarily high voltage that makes noise, that affects low level circuits. For example, the EM field of the PRIMARY wiring driving the coils is a very "big" factor. This gets induced into other wiring just like a transformer

Google up "Faraday shield"---shielded, balanced sensor wiring with one end of the field only grounded
It is not necessarily high voltage that makes noise, that affects low level circuits. For example, the EM field of the PRIMARY wiring driving the coils is a very "big" factor. This gets induced into other wiring just like a transformer

Google up "Faraday shield"---shielded, balanced sensor wiring with one end of the field only grounded

you are correct lots of EMI from coils charging and discharging.