Disconnect the tack then. Iffy tach and wiring to it can to same as a bad filter.
MSD is crap hype to start with. On a stock engine way more so.
And Not just the "box."
Many MSD and Accel parts are crap and been so for 20+ Years.
Is made to sell to fools that think GM Ford and others are too stupid to make engines and ignitions to run them. That's why GM "stupid" engineering eats Millions of $ per year...
Is likely burned the cap and rotor. Replace both.
If plug wires are 3+ years old. replace them too.
If coil is MSD/Accel... replace it. Use Wells or AZ (AZ ignition parts are Wells.)
And use standard or maybe Platinum plugs. Simple Platinum not gimmick plugs or Bosh 2 or 4 ground tips. (I mainy use better plugs only because has better metal parts that don't rust easy.)
Check base timing too. Iffy base timing will cause ECM problems to set actual timing to run the car.
[This message has been edited by theogre (edited 06-13-2019).]