Aftermarket cat converter advice needed
 

Think my cat(s) are finally biting the dust. I replaced both o2 sensors around 3 years, 40k miles, ago and that caused the P0420 to go off for a short time but it's mostly remained on during that time.

Driving home the other day when trying to accelerate up a hill at highway speeds. Downshift and RPMs around 3500 when all of a sudden I get this horrible grinding, metal fragment, screeching sound that sounds like it's coming the area near the cats. Back off the throttle and noise stops but then I have to give it a lot of throttle to maintain 60mpg going up a slight incline. Took the backroads home and made it home fine going around 50mph.

Searched around a bit and found a thread where the user removed the front o2 sensor and noticed improvement during acceleration, replaced the cats and he was good to go. I did the same for mine and noticed some definite improvement but didn't drive as easy as it should.

Any advice on which cats to go with? I've got a 2001 supercharged 3.4 v6 with 2 cats. It seems most people go with Magnaflow, Walker, or Eastern. If you have these how are they holding up? Curious about part numbers and if you've replaced with aftermarket cats did you use the direct bolt on fit or the universal weld on fit? Thought about having them welded on as I don't feel like dealing with the rusty PITA bolts. I would have a local shop weld them on most likely. They just recently charged me $30 to have my new Borla muffler welded on.

Any advice would be greatly appreciated. Thanks!

I have a Walker. Heat shields may rust off over time. Avoid the cheapest ebay POS.

Did you go with the direct fit?

Yup. I don't bother with muffler shops anymore. The prices they charge around me end up breaking even with direct fit.

I used Bosal direct fits from RockAuto last year, they bolted up perfectly and have been working well so far. Nice thick flanges and good welds everywhere.

I installed Walker cats also (Cali with 2), stainless bolts and double lock nutted entire exhaust.

The most common cause of P0420 is an exhaust leak near the cats or O2 sensors. The flanges on Toyotas always rust to the point that the gaskets won't seal anymore. Sometimes the converter shell rusts out where the heat shield is welded on. If the converter has broken apart inside you should be able to hear it rattle when revving the engine in neutral or just banging on it with your fist or a rubber mallet. You could also remove it and look inside to see if it is plugged. A really plugged converter will cause a loss of power at first eventually causing stalling or even no start. Removing the O2 sensor on a totally plugged converter will allow it to breathe enough to be driven, but will not run perfect due to one of the most important sensors in the engine being removed from the exhaust pipe and thus no doing its job. If you have to replace the converter I would recommend the Magnaflow. It's high flow, all stainless steel and 2.5" all the way through.

I put on the Eastern CARB compliant direct fit set from Rock Auto and they have been hold up well for about a year and a half so far.

How did everyone deal with getting the nut or bolt off the upper right of the flange as as you look from the bottom? It's so tight in there that I have ruined the nut and can't get it off.

Acetylene torch and six point swivel sockets. If you don't have that stuff take it somewhere.

If you are junking your front cat, you can cut it off with a SawsAll near the studs. And any nuts you wrecked, use a Map Gas bottle torch heat the stud/nut up repeatedly if needed and wiggle it back and forth til you can unscrew it with Visegrips or whatever will grap it, stud and all, or if stud stays on, you can keep it on, but nice if you can get it out. Autozone sells a stud kit for these with brass nuts thats wont rust up....but the stud kit has different threads than the original, so you can't just use the nuts.

Those brass nuts strip before the required torque. I tried them


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That P0420 code is also caused by antifreeze. And there is only one place that comes from. My 97 gave me that code constantly from a rusted cylinder liner allowing antifreeze consumption.

Same CAT and a rebuilt engine the readiness monitor for the CAT cleared in 6 miles of driving at 60mph. It’s only been around 1000 miles since the engine swap but as fast as the readiness monitor set I’m not worried about a bad CAT


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No problem for me on multiple uses, and removals.

I wish I could say the same.


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