P0420 can indicate a clogged cat or a failed o2 sensor.

 

Kind of a tricky one. Looks like the P0420 code is most often a bad cat so the question is why is the car still running poorly with the stock cats reinstalled.

It could be the aftermarket cat/cat installation hosed your O2 sensor or it could be the ECU has modified the running config to adjust for the bad cat it sensed.

First/cheapest thing to do would be to drive the thing to see what happens with the codes. If the ECU sees the cat is fine again it may restore the config itself which may solve your problem.

Any chance you broke or d/c'ed a vacuum line while you were working on it?

 

Okay so I took the car to the dealer and after a week they told me my cats (stock ones that were completely fine before I swapped them out) are clogged. I’m kind of skeptical. They said the O2 sensors are fine. It’s just kind of hard to believe that I had 2 cats go out in a row. But I am at 101,000, and the average lifespan of a cat is about 100,000 miles. I guess I have no choice but to get new cats now. Unless anyone else has some suggestions.

 

Berk or kinetix

 

Get a new set of FI's. About $650 at fastintentions.com.

 

Nah, Im gonna go with Kinetix. Kind on a tight budget right now.

 

Man, neither of my stock cats made it past 25,000 miles. They were both replaced under warranty. My service rep told me that was an unusually common problem with the 350Zs.

 

Weird. I’ve never seen that happen on any car before. Thanks for sharing

 

Just hollow out the insides of the used aftermarket cats that you purchased... You might need to add 02 extensions so you won't throw a code...


I would think the more likely explanation for your problem is...

You put on clogged aftermarket cats, your car got pissed and through the code.... You replaced the clogged cats with the stock cats that had no issues.

The code persisted, the dealership read the code and came up with the clogged cat conclusion hoping to make a quick $ on some new cats.

Did you unplug your battery for a few hours and let your computer reset after you swapped back over to the original cats?

 

Maybe they weren't properly tuned when you installed them. Or maybe it's just because they're used.

 

I reset it for about 20 minutes; all the trip readings cleared so I assumed that was enough. Gonna try to unplug it overnight and see what happens. Still no code or anything.

 

Do you have stock exhaust from the cats back?

Did you look inside the aftermarket cats before you installed them?

Could the previous owner packed a plastic bag or packing material inside that you forgot to remove and now its stuck in your y pipe or muffler?

 

I do have the stock exhaust. The fast intentions cats were fine when I bought them. I’ll check the y pipe but I don’t think the owner put a plastic bag there haha. How could I check the rest of the exhaust withoht taking it to a muffler shop and having them cut it up though?

 

I would check the y pipe and the mid pipe with a wire as those go straight through. If they come back clean and clear. I would just disconnect the muffler all together and see if your problem goes away.

When you looked inside the aftermarket cats was the honey comb section still in good shape?

I know I have put plastic bags inside exhaust parts to keep mice from forming a habitat inside of them when storing them outside in the shed.

Better yet just remove the mid pipe, and muffler. put a wire up both ends of the Y pipe make sure theirs no obstruction in that. Then take the car for a ride around the neighborhood and see if you can go over 5000 rpm again.

 

Thanks for the suggestion. I’ll try that and see what happens. And the honeycomb initially was fine but when I took it off it was completely destroyed on the driver’s side cat.

 

Easier.... just go to Pep Boys and pick up a bottle of "Muffler Metamucil".

 

Just buy test pipes and be done with it.