when they put cats on the engines mate

so you've got a mix and match, but they started to do them in about 90 with them becoming more and more common as a granda engined version

the sierra's didn't get them until they were supposed to have them as i don't think they were required by law to have them and were only "optional" at the factory

if the engine otyu are looking at is post 92 though it would most likely to have had hydrualics in it

they are crap though for anything performance wise so most cam kits will come with solids you can adjust