[Garland]

For the third time today my V6 backfired on start up "popping" the plenum off. Several weeks ago after the last time, I pulled off the valve covers and checked all of the timing variables. Cams, distributor, etc. Everything is correct. Today when it blew, the plenum cracked the plexi cover as mine is a Maratona. Any ideas as to why this would be happening? Car runs fine otherwise. Is not difficult to start etc. Again, logic would say it has to be timing but it's not. I'm puzzled. Ideas please.