94 z-28 idles rough when you try to accelerate while driving it has no power and valves rattle / spark knock. I tried to pull the codes OBD 1 the cooloing fans come on but the light does not flash at all not even the 12 check code. Anyone have any ideas ??????????
thanks

 

umm check the cat. It may be clogged

 

You can NOT flash the codes on the SES light on an LT1 newer than 1993. You need a "real" scanner, or scan software to pull the codes.