So last week or so, I have noticed that my new S10 does not have this secondary air injection system like my 2000 Blazer does. I'm kind of curious as to how some trucks have them, and others do not. Both of mine have the same engine, same trans etc. Just different body styles and 2 years difference.

if they can meet the necessary emissions without it count your blessings, that was my biggest headache on my uncles sonoma. the last vehicle i had personally is the firebirds original engine had it. my 89 c1500, bonnie, 99 yukon, 03 monte none of those have that

Yeah all depends on what year it is, there'* two or three versions of the 4.3. One is a VIN Y and one is an X. All depends on emissions and stuff like jwfirebird said. But I think the Blazer and S10s are the same, the full size trucks are slightly different.

Shaun is that the engine vin code? X or y? Last I knew, my vin was a W.