Having a problem finding any topics which touch on this. I’m the proud owner of a 2006 M35X with 150,000 carefree miles logged. Recently I’ve heard some rattling from underneath the car. Because the heat shields on both cats were rusted through, I figured that was the problem. Simple fix right...wrong after a couple of screw clamps the rattle is still present. Believing that one of my cats have gone bad, I was hoping somebody on this forum may have already “experimented” and came up with a good replacement cat cheaper than the crazy OEM price

Thanks in advance

What state are you in? Do you have emissions testing?

If the heat shields are rusted through, there may be other issues (not internal cat failure) causing the rattling.

These are 49 state legal:
https://www.maperformance.com/products/ ... -kx-de-hfc


Anything other than the OEM cats are "illegal" in CA. Or maybe an aftermarket company may have m,ade a CARB legal version sometimes in the past few years since I looked.
Though, some of the high flow cats will still pass "sniffer tests" even in CA. Which to me means they should be perfectly legal if they are still passing such strict smog ratings, but because they dont have a specific CARB number stamped on them they are technically illegal.

I share your grief, mate. I assume you also have the related P-code showing on your dash and you have actually confirmed by visual inspection that there is nothing else causing the rattle. It is possible to buy CATs that will fit exactly like the OEM part or 'universal-fit' CATs that can be made to fit with additional pieces. However, many aftermarket CATs, even if they fit perfectly, may still trigger the P-code and / or not pass emissions inspection because they do not perform as the OEM parts. If you can confirm those CATs have worked for other Infiniti owners without triggering the codee, I'd say they are worth a try.
If you're wondering about actual OEM parts, you can buy OEM CATs direct and save the exorbitant mark-up from dealer supplied parts. Here is the thread I made after going this route:
post6772002.html#p6772002

I live in CA so I couldn't get just any aftermarket CAT. I had to go to Ebay and find a used one from another 07 M35x. Paid about $220 I believe. installed one about 2 years ago and haven't had any issues with it. Still pass smog in CA. I am tempted to get some high flow cats but most sites state they won't ship to CA but I wonder how true that is...

Thanks for the quick and informative reply's. I live in Ohio and have been up under the car numerous times pulling on the other components and heat shields and even though I haven't got the P code, everything is still pointing toward a bad cat.

Vanv wrote: ↑

Tue Nov 12, 2019 11:49 am

Thanks for the quick and informative reply's. I live in Ohio and have been up under the car numerous times pulling on the other components and heat shields and even though I haven't got the P code, everything is still pointing toward a bad cat.

I would run the car by one of those auto parts stores and have them run for codes. Seems odd to me that something like a CAT would not produce some sort of oxygen, emission, or some related code.

Larz wrote: ↑

Wed Nov 13, 2019 6:27 pm

I would run the car by one of those auto parts stores and have them run for codes. Seems odd to me that something like a CAT would not produce some sort of oxygen, emission, or some related code.

My friends Q60 had both cats go bad, the second one two weeks after the first. It did not throw any codes or lights on the dash, just a rattling sound under the car and bad smell from the exhaust. Thankfully for him both cats were replaced under warranty.

to also add, I never got any codes either. I just got a bad rattle from the passenger side cat due to the honeycomb inside dislodging from its seat. No bad/funny smell in my experience.

I reckon as long as the flow of exhaust isn't badly restricted, no codes get logged. I got codes and the infamous but not strong rotten egg odor at the exhaust tips. Never any odor inside, jut near the tips. My service rep told me at the time that some aftermarket CATs might fit fine and work fine, but may not be compatible with the computers and throw codes for that reason alone. I dunno if that is documented fact or just repeating unverified comments from other mechanics.
If I weren't ok with the cost of new OEM from the discount peeps like infinitipartsonline, I'd think seriously about getting used CATs from a totaled M that matches your year and engine.

Yeah, thats the route I went. I didn't want to pay OEM prices so I found one on Ebay from a totaled M, and found the one for same year and make and was CA carb compliant. I've been satisfied so far with my last purchase. Haven't had any issues or smog problems.