Gentlemen (and ladies?), I'm looking at getting rid of P0420 - "Catalyst System Efficiency Below Threshold (Bank 1)". The check engine light is on most likely because of the high-flow catalytic converter that was installed by the previous owner. I have no idea if it's a junky cat or not. I really need to pass inspection, and here in New Jersey, you fail emissions before they even perform the actual test if your CEL is on.

Option #1: ZZPerformance u-bend delete: ZZPerformance - Ubend Delete #ZZ-UBENDD

-Should I do the spark plug non-fouler trick to space the rear O2 sensor out of the exhaust stream? Does that mean I specify with or without rear O2? Or should I get an O2 emulator?

Option #2: ZZPerformance downpipe: ZZPerformance - ZZP Downpipes #ZZ-GPDP

-I'm naturally aspirated so I need the 2.5" piping so as not to lose low-end power. I also clearly need a cat on it. Do I get the aluminized piping for $169.99 or the 304 Stainless Steel for $219.99? Most importantly, should I specify "Add rear O2 bung in offroad pipe"? Does that mean if I go without the bung or it's simply not applicable on my downpipe, then I need to drill and install my own spaced O2 or bung?

-Are there less expensive brands for downpipes?

If you have had experience buying ZZP's downpipes before, please help! THANKS.

 

Dub - If you are interested, I am offering some minor PCM services, which include deleting the P0420 code associated with the high flow and non-OEM cats (see link below):
https://montecarloforum.com/forum/pr...impalas-42773/
PM me with any questions you may have regarding what I am willing to do.

Let me try to answer your questions:
1 - If you intend to do the O2 anti-fouler trick, you must have an O2 bung.
2 - If you buy a ZZP down pipe, it has a U-bend delete built in.
3 - Simply adding a U-bend delete will not resolve the code condition
4 - If you get an O2 emulator and never plan to re-install an O2 sensor, you can get a pipe without an O2 Bung.
5 - You can go aluminum OR stainless, up to you.

I have a ZZP 2.5" downpipe with high flow cat and my P0420 code is deleted (no non-fouler, no emulator, clean appearance to any onlooker). If you want to see info about my ZZP DP install, go to my web page here:
'04 Monte Carlo SS - ZZP Downpipe

If you order a ZZP down pipe with cat, you run a high chance of still having the P0420 problem. No matter what, you MUST order the down pipe with an O2 unless you plan to go for an emulator (as the emulator would not attach to the cat).

 

Maniac, you're the man. Thanks for so much help and information. Here's what I'm thinking...downpipe w/ cat and an O2 bung. If it comes with the O2 bung, does that mean the O2 sensor comes with it?

At this rate, I'll probably get P0420 deleted from the PCM.

 

If it comes with an O2 bung, that's it. You need to supply your own O2 sensor. When I did my ZZP DP, I just pulled the factory O2 sensor out and popped it into the ZZP DP.

Fair warning, O2 sensors that have been in use for a long time might be hard to get out (mine had less then 60,000 miles on it I think when I did my ZZP DP swap). When I've changed bad O2 sensors in the past I've had some break on removal OR I could not use my O2 sensor socket, so I cut the cord so I could fit a deep well on the old one. When you do this, you will have the O2 still in the old DP, out/off of the car, so you could put a closed-end wrench on it and break it lose (something hard to impossible to do with it in the car).

Also, when I did my ZZP DP, I optioned for the O2 extension cable, turns out I sent it back with my core return for a credit (which ZZP did with NO issues).

Lastly, since ZZP only had interest in the old cat, not the rest of the DP, I used the sawzall and cut it open. The factory DP is double walled and not as open as the ZZP one (I believe the factory one is about 2-2.25" on the inside diameter due to the double lining).

Hope that helps

 

Okay, getting the old O2 sensor out wasn't exactly happening when my dad and I tackled the project. Literally rusted onto the U-bend. Good tip about the old cat because the $50 rebate really makes the whole process worth it. Do I need new gaskets though? You said that you got them for your car.

 

Do you have any metal recycling plants near you?

You can get a good amount of money from a cat. Also zzp doesnt refund $50, it is a coupon off your next order. Might be worth looking at a local place to sell the used pipe.

 

It is in your best interest to replace the gaskets. If you don't you are running a gamble on having an exhaust leak and having to mess with this all again.

BTW - Chibi is right, ZZP gives you a $50 coupon code for the old cat, not a $50 refund.

 

It's probably much more worth it to try and get it recycled then. I'm sure I could find a place for the cat then. Would I be looking elsewhere to sell the pipe separately, or would most places take both metals?

 

They would probably take the whole pipe off your hands