You could try a timing light to check for sure. Other things can cause a backfiring condition, a too rich or too lean fuel mixture can cause it. A compression tester would tell if your valves or pistons are damaged or if you have an intake valve that is too tight or cracked. If all else fails you can change it over to a carbureter and change the distributor to the old style, like a 1975 Chevy which pretty well takes the computer out of the equasion. Good luck
Joe