D_Toro.
Read your initial post again. You replaced the ECU because it was 'bad for a very long time'. What does 'bad mean? What symptoms?
I doubt it is the ECU if a replacement did not fix the problem.
The timing can change veeeeeery slightly with different ign systems, but not enough to cause popping.
Forget the nonsense about getting a MSD 6X box [ unless you have a 800 hp engine ], that will do nothing other than lighten your wallet.
I would check these things, regarding popping in the exh:
- dist cap & rotor for carbon tracking
- plug leads [ & coil lead ]. Replace if old or suspect.
- try another coil
- measure the bal resistors, cold, engine off, one end disconnected. Should read 0.5 ohm & 5 ohm.
- make sure with engine running that you are getting 12v at the ballast resistors.
- make sure the pick up wires are twisted, kept close to ground & that they are kept away from the coil [-] lead & HT leads.
Other things can cause popping in the exh; burned valves, valves not seating, worn cam lobes, carb.