You may not have received a response in 4 weeks because you incorrectly posted in the "show off" section. Having "Trouble with my car" as your title is very vague and doesnt attract helpful attention either, which is why I changed it. Keep these things in mind in the future.
Now, there are multiple reasons why it could back fire so provide more details, which is also helpful in attracting assistance. Has your engine backfired since then? Is your check-engine light on? Are your spark plugs and wires overdue for replacement? Are you using 87 octane fuel?
