I have a 95 blazer and needless to say its running like complete shit. It has the 4.3 ltr vortec cpi motor. I figured itd be the cpi spider injector but theres no unusual gas smell coming from the motor and no fuel on the dipstick the shop i took it to is saying o2 sensors are the culprit but i didnt know they could do that, when i mean it runs like shit it spits and sputters and backfires while driving, backfired so bad it blew up the muffler if anyone can help me on this it would be greatly appreciated, thanks in advance