Roughly 1 week and a half ago, the check engine light came on. When I checked it was the p0420 code (catalytic converter), which made sense, since lately it felt like it's been getting plugged up some. (high revs with little torque/hp compared to the past).

Anyways, put it up on a lift at the shop I work at and sure enough, the cat's bad. (at 137,000 miles, I'm not too surprised). My question is: should I go along with the OEM GM cat, or an aftermarket high-flow cat (and which would be the best for the 06' 3.5L?), or should I just say to hell with it and do a cat delete? (yes, I know, with the high-flow cats and cat deletes, there is almost a definite result of a code from the second O2 sensor)..

So, I need ideas/input on which would be best performance-wise, sound-wise (if it will effect the sound at all). *I already have dual flowmaster 40 deltas with no resonator*

 

From what i understand (which is not much), the high flow cat will be a great performance and probably sound increase. As far as codes being thrown im sure its quite possible if you have a lot of mods. OEM is going to be expensive where as aftermarket is probably cheaper. Aftermarket will probably not last as long as the OEM which so far for me is over 100k mile on stock OEM cat. Though i believe i too am having some cat troubles but no codes.

If your planning on doing a cat delete which will more then likely be the cheapest route be away of your states emission laws! Some states are pretty strict. Also seeing as you work at a shop im sure youve seen the difficult location of the cats on our cars, they are on a sort of difficult to reach bend and my muffler shop told me they couldnt install a high flow cat i bought and had brought to them to be installed because of the difficult location of my cat(though i call bull****).

It seems like the cat on monte carlos fail quite often, ive seen your other thread about E85 and if anything it might just be a band-aid for your cuttent cat problem. I would suggest doing a back pressure test before you go ahead and replace your cat, unless your like me and didnt care wether the cat was bad on not and just wanted that damn high flow cat!!!!!!

Good luck!!!

 

Honestly, I've been thinking some more about the cat-delete and although I do like the increase in airflow/torque, I don't like the smell of running straight piping instead of the cat.. stupid as that sounds, I not only want my car to look good, and sound good, but I don't want all of the people I pass to wonder why it smells like sh*t hahaha.

So, I'm just going to go with a magnaflow high-flow cat that's at my shop. Mounting it won't be a problem because I have no resonator I'm just going to replace where the cat is/the bend after it and then put the high flow cat where my resonator used to be since there's now a 2.5/3 foot gap of just straight piping there? should be pretty easy, half hour to an hour tops. and for the O2 sensor problem, I have adapters so I can put one in the pipe pretty much anywhere I want.. and the magnaflow shouldn't set off the P0420 code so I should be in the clear with the check engine light.

Since the code is gone right now, I'm probably not going to get around to this until next week or the week after, but I'll post an update whenever it's done

 

Sweet man, the perks of working at a car place are endless huh haha, and yeah LMFAO you'd be spewing rotten egg smell at everyone behind you if you straight piped!! I think the magnaflow is your best bet, also when you repost if you take any pictures of the work please post em up!

 

When I took my Monte to a local shop to talk with a guy about options for changing my exhaust, I asked him about installing a high-flow cat on my car and the first thing he said was that I would get a code because of the location of the second O2 sensor after the cat. But from what you wrote, it sounds like you might be able to work around that problem. Let us know how it works out.

BTW, how the heck do you have 137,000 miles on an '06 Monte? Damn, I thought I did a lot of driving! I've got a little over 87K on mine now.

 

haha yeah, I get that a lot.. I like to drive a lot. till I get my motorcycle insurance renewed, I'm driving this for deliveries as well.. so that adds up quickly.