T56MaxTorq said

The backfire occurred after the coil change and ignition timing adjustment. I’d put the old coil back on. But then you say you have a 4 point ballast. Any msd coil is designed to be wired to 12 volts, not a current limiter like a ballast. The ballast was originally designed for an older style coil that had a different amount of turns. You backfired because you don’t have enough spark energy (due to the ballast) at higher rpm to light the mixture and a full mixture dumped into the headers instead. Spark energy is weaker at higher rpm, greater number of cylinders/plugs, dwell setting, temperature, coil turns, primary voltage, etc. in this case, your coils primary voltage is probably around 6 (if I can remember back that far) when it needs to be 12. Which in reality it’s operating at 14 when the generator is helping charge the battery.

You need to bypass the ballast for the coil so it is fed 12v w/ ignition is hot. There is a lot of mopar ignition ballast resistor removal threads on the internet if you need a walkthru. You can also simply use alligator clips and jump the resistor at the terminal lugs but a full ignition system rewire is what I’d do. Recheck ignition timing after any adjustment and try again. I hope this is your issue

Click to expand...