L30 - 5.0 vortec, L31 -5.7 vortec, L35 - 4.3 vortec.
As sown above the L31, 5.7, has one O2 senor ahead of each cat, and one O2 sensor behind each cat, 4 total. The drawing is bad example. I don't know why they have 3 sensors ahead of one cat in the 4.3 configuration. The " NA1 " is the RPO option for what emissions level it came equipped with. ( NA1 Emissions level less than 8500 lbs.)
The TBI engines, OBD1 and earlier have more simple emissions systems. The LO3 -5.0, LO5 - 5.7 have single cat.
So if you have to comply with emissions or just choose to be compliant, knowing what level or RPO option will simplify your choice. My friends 98 Tahoe from Texas has cats in different location from my California emissions 98 Tahoe. I can understand adding more for stricter rules, but other than thermal activity, changing the location of cats has me confused.
So when your looking at the parts diagram the notes are often using RPO codes for model application. NA1 less than 8500. NA4 above 8500. NB2 emissions CA tier 2. And so on.
As sown above the L31, 5.7, has one O2 senor ahead of each cat, and one O2 sensor behind each cat, 4 total. The drawing is bad example. I don't know why they have 3 sensors ahead of one cat in the 4.3 configuration. The " NA1 " is the RPO option for what emissions level it came equipped with. ( NA1 Emissions level less than 8500 lbs.)
The TBI engines, OBD1 and earlier have more simple emissions systems. The LO3 -5.0, LO5 - 5.7 have single cat.
So if you have to comply with emissions or just choose to be compliant, knowing what level or RPO option will simplify your choice. My friends 98 Tahoe from Texas has cats in different location from my California emissions 98 Tahoe. I can understand adding more for stricter rules, but other than thermal activity, changing the location of cats has me confused.
So when your looking at the parts diagram the notes are often using RPO codes for model application. NA1 less than 8500. NA4 above 8500. NB2 emissions CA tier 2. And so on.
