A recent thread inspired this. I've got a 91 blazer, 350 with no accesories. The accessory belt only powers the water pump, power steering and alternator. There's no A.I.R. pump, or A/C. Should there be an A.I.R. pump? Furthermore, just before I bought the truck it had the exhaust replaced and the new exhaust came without an o2 sensor. Is there supposed to be one? Where in the harness does the o2 wiring feed back to if there is one? That would explain the poor fuel economy and rough idling issues I've been having, but I'm stumped as to why there isn't any check engine light glowing? Thanks for your help, Chad.