hey everyone, i have a 2005 2dr Blazer 4x4 5spd manual. I replaced one of two convertors recently (the bigger one down stream) but ive still off and on been getting a po420 code catalyst efficeincy below threshold ( bank 1). Would they maybe be cause because the small Cat built into my Y-pipe is bad? If that is my issue will i get a continuous code if i delete the mini cat in the Y-pipe?

 

The cat that is setting the code is the one directly infront of the O2 sensor. The code may still be valid if a universal cat was used versus the Direct fit ones.

 

Below is an excerpt from an article about O2 simulators on eBay

Truth about O2 simulators | eBay

"The computer maintains a constant switching from rich to lean to produce a stoichiometric average. This method eliminates the need for air injection into the catalyst bed, and increases catalyst performance. The converter contains a variety of metals which carry out the reaction process, but it also contains a variety of other metals and compounds that assist this process, including a variety of oxygen storage compounds, typically either Cerium Oxide or Zirconia Oxide. Because of the reactions that take place, the waveform of the downstream sensor on a vehicle is typically a much more steady signal that is quite different from the rich to lean oscillations of the upstream sensors. If the converter is missing, or is no longer functioning, these reactions do not take place, and the downstream sensor will "mirror" what the upstream sensor does. The computer will measure the signal from the rear sensor, and if it is outside the acceptable limits, the computer will set the CEL"

You could try an O2 simulator which is nothing more than a spark plug non-fowler sold at parts stores for a couple of dollars. I made an electronic one out of resistors and diodes, but it didn't work.

Good luck, Shimaze

 

it was a universal cat that was installed in it.

 

The small cat is only to heat up the big cat faster for quicker efficiency. Bank one has nothing to do with the cats if memory serves, it has to do with the burn efficiency of, I believe, the passenger side cylinders.

I'm sure someone much more knowledgeable will show up very soon.