strange 5.7 vortec factory exhaust system

[99xcss4]

dose any here know any thing about 5.7 vortec dual cat exhaust system only having 3 o2 sensors I had all ways thought they had 4 of them?

 

[Caman96]

The downstream right near passenger side frame is kinda hard to see.

 

[Dravec]

Should have 4. All 4 that I've had were a 4 sensor system.

 

[99xcss4]

thanks I will send the info on its way

 

[b454rat]

Or it's a 305.....

 

[L31MaxExpress]

Or it's a 305.....

305s are single cat with a Y pipe

 

[b454rat]

meaning it won't have 4 O2 sensors lol

 

[GoToGuy]

All the Calif. Emissions have two cats, 4 each O2 sensors.

 

[L31MaxExpress]

meaning it won't have 4 O2 sensors lol

The 4.3s and 305s both have 4 02 sensors. 1 behind each manifold, 1 after the pipes merge in the Y-pipe ahead of the cat and 1 after the single cat.

 

[L31MaxExpress]

All the Calif. Emissions have two cats, 4 each O2 sensors.

They do not, some of the L31 2-door Tahoes and the Vans have a single cat in both California and Federal emissions. California adds an electric air pump.