Contour Enthusiasts Group Archives Forums General Troubleshooting CEL P0420 and P0430 - bad precats?

I am getting the codes P0420 and P0430. These came on just after I did the TB optimization. I don't know if this is a coincidence or not. I have recently replace the downstream O2 sensor in bank 1. I am getting slightly lower mpg - about 26 vs. 29 for highway driving. Also, I get a sulfur smell when I stomp on it. I have a new (January 04) main catalytic converter that came with the Brullen y-pipe. Based on what I've researched this does sound like pre-cats are going out. Anyone agree? By the way, I have 106,xxx miles.

I am planning to do the gutted precat mod. I need MIL eliminators or something like that. Does anyone know what the proper term is for them, where to get them, and where to put them (up or down stream sensors)? Does buckshot still sell "optimized" exhaust manifolds?

Thanks in advance for your help.