1995 Buick Roadmaster 5.7L . Recently replaced timing chain , optispark , ignition coil . Recieving code 16 from ecm. vehicle fired up and ran twice before completely re-installing the water pump and secondary air pump. Put the rest of engine back together and no spark coming from optispark and no low resolution square wave coming from optispark !! Any info or ideas on where to go from here will be greatly appreciated . About to pull my hair out !!