The front cats are mounted pretty close to the exhaust manifolds and its a tight fit there to be welding in new ones without removing the pipe assembly. Plus finding a cat that will fit and the engine management will tolerate might be an issue. Aftermarket cats can be a big pain in the a$$ on a lot of newer vehicles. I've had lots of experience in this. If you go with an aftermarket cat assembly be sure the installer will stand behind it if the problem returns. We would usually credit them if they agreed to upgrade to OE cats and pay the difference on the parts and pay to install again. We also made this clear before even doing the job the first time. We would send the aftermarket cat back as a defect for credit as it wouldnt work properly.
Another thing that can work is to install a thing called a spark plug anti fouler. Its a small fitting that moves a spark plug out of the combustion chamber a small amount to prevent oil fouling on a cylinder that is using oil. Its an old school device that can be used to move the post cat O2 sensor out of the exhaust stream to stabilize the voltage signal it sends to the ECM. NAPA sells them and you need an 18mm one for the larger spark plugs. You have to drill it out a bit so the sensor bulb will fit. You might even find one online thats made specifically for this.
When a cat starts to fail the post cat O2 sensor starts to mimic the precat sensor and that triggers the sucks to be me lite. If you scope the sensors on a healthy cat the precat voltage will be crossing over the .5 volt mark .1 to 1.0 volts regularly and the post cat will stabilize around the half volt mark and stay there. Readings on a bad cat will be almost the same.
Unless the vehicle is a Toyota, then the precat air/fuel sensor will fluctuate between .1 and 4.95 volts and the post cat sensor (still called an O2 sensor) will still read about .5 volt on a healthy cat.
Could also have a tuner turn off post cat monitoring if thats possible.
Sorry so long.
