Causes of Backfire

[jss06c6]

Gents, I think a discussion as to the causes of backfire might be worthy of a new thread (unless this is covered in an older thread). I suffered a backfire which blew off the PCV connection and the Gas Tank Purge Solenoid connection underneath the plenum. I've had the car since 2013 and have never had a backfire. It had been sitting for a couple of weeks in my shop and I needed to move it. When I started it up, it immediately backfired. I waited about 30 seconds and started it again. Fired right up, but belching lots of smoke out the back (rich fuel!) and then settled into a high idle (1200 rpm). Drove it, no problems at all, but had high idle. That's another thread..

So, I was thinking about what could cause the backfire. When I took the intake horn off, I could clearly see where pressure exhausted around the TB valves. Only way this could happen would be that a cylinder fired when there was fuel present and an intake valve was at least partially open. So how can this happen.. I'm guessing that the LT-5 employs a batch fire logic at start up (opposing cylinders get spark at the same time) rather than sequential spark
& fuel injection as newer engines do. If this is the case, how is backfire prevented from happening again when some raw fuel is sitting in a cylinder from engine shut down?

Do we tune this out? I know Marc employs an Antibackfire change in his tune (this is in my car) when headers are installed (like mine).

Listening to learn from the experts.. Seems to suggest with better control from the ECM (MS3PRO or other), we would be able to properly eliminate this issue.