Funny you say that. I had a knock off dizzy in my car and I upgraded to msd. Now my tach jumps up and down randomly. I did the twisted wire, separated the wires to the box added the grounded shield wire and still not fixed.
Yes they both work the same way. I thought that the noise was coming in on the tach wire but then after all of the shielding and wire twisting I still had a RPM Nose Fault. I then (because of my electronics background) figured that it must be coming in on 12 volt supply wire so I made that filter. The problem hasn't returned. It's easy to make.
Calls to msd results in someone talking down to you. No help whatsoever. Ok Msd expert tell me why the knock off works fine. No answer.
just wondering if the fitech is seeing that same tach signal