Hi Been working on My Son's first car. 2000 Chevy blazer lt 4.3 v-6. It has 151,000 on it.We have had some issues but have been moving on them. Had a misfire in cylinder 2. Replaced cap, rotor,wires an plugs. Some improvement. Leaned toward injectors. When testing fuel pressure immediately after running vehicle found it was zero. Replaced spider injector. Btw 3 were leaking into the intake u could tell by the factory clean lower on half of the manifold. Truck runs great! Had check light come back for p0420 immediately. But figured it would because of all the cleaner and carbon that got by, I did roll up full paper towels and blocked all intake ports for fear of dropping something down there, and used shop vac to clean up. I removed all the paper towels and verified they were full pieces. Cleared code drove approx 100 miles runs great. Connected code reader and came up with p0410 secondary air system. Removed pump to check for water issues found none. Researched and found info on gm bulletin about air pump. Everything checked out ok, but the "parts changer" that owned this before connected the air pump intake tube to the coolant reservoir overflow tube! Routed that down and moved the intake tube to the inner fender where it is not subjected to water. Cleared code. Runs great. Now the question could the intake tube suck in vapors from the coolant and psych out the computer? I have spent a lot of time and money on this, but I have only 1 son and one first car for him. Remember your first car, I can't say or think that with out smiling. Thanks for taking the time to read this and all of the info from these posts. Mario