We have a 2004 Malibu RLXi. Runs great except that once every 35-45 passes it backfires. This has literally been going on for 2 years, in the shop about 11 times, and the guy still has not fixed it. Rough estimate of what has been replaced:
Entire ignition system
ECM (2 times)
Filters in injectors
Much more but this is all that I am 100% sure of
The current theory is that the a fuel injector screen was clogged so it was dripping gas instead of spraying a mist. Adding up over many passes it caused a back fire. Mechanic changed the filter in all 8 injectors and said on one of them it was more dirty than the rest making him think that is the issue. He said if it keeps backfiring it may have damaged the injector bring it back and we will put in a new injector. It is still backfiring. We have not yet taken it back to get the new injector, but my question is weather or not this sounds like it could be causing a backfiring issue.