I had the catalyst issue a few years back. Replaced the cats/manifolds and the 02 sensors. Was good for a while now I’m getting the codes again. I was told if I used aftermarket parts I’d need to install 02 sensor spacers due to the computer being extremely picky with aftermarket stuff.

Has anybody used spacers and if so what would you recommend.

Thanks in Advance

V6 or V8?

You say you replaced the manifolds and O2 sensors a few years back and are getting codes again. My first question is did you use OEM parts or aftermarket replacements?

Aftermarket parts work but will not last as long as OEM parts. Sensors should be replaced with Denso or OEN, which happens to be Denso. Aftermarket cats/manifolds work for a few years but the material for the cats is no where near as good as the OEM stuff and they don't last.

Using O2 spacers is basically a band aid for the actual problem. Replace the parts with OEM parts and make sure the rest of the maintenance is up to date on the vehicle.

It’s the v6. I did use aftermarket manifolds/cats with denso 02 sensors. I replaced these 5 years ago, I would have assumed they would last longer then that?

Aftermarket cats can fail within 5 years or less, or you might get lucky and they last longer. OEM cats will most certainly last around 100k miles or more. I've got over 337k miles on my original OEM cats with my V8 and They are just now giving me issues and throwing O2 codes, even with new Denso sensors. I'll be replacing the manifolds with OEM again. Little more expensive but they are proven to work and last longer than the cheaper aftermarket ones.

I'm all for band-aids in this case. Certainly not putting OEM cats on my rust bucket. I'll be trying the spark plug spacers on mine that has an intermittent p0430.

I did get a cat code last winter/spring a couple times below 40 degrees, but it would go away if it warmed up that same day. Guessing there's a small leak I couldn't seem to find, but ordered DT long tubes and a MF Y-pipe. Will most likely be installing headers this fall. Got one of those "Last sets" of DT longtubes I always read about.

Yeah check for the donut leak first. I bought replacements and got the passenger side on first and the stock with 225k miles looked perfect.. but the exhaust donut looked bad. Just barely enough to cause the light to come on. Now I don't know if I should just replace the other and go from there and scrap the OEM cats for cash..

I’m in your camp on this one. Especially now that we don’t have emissions anymore I’m less worried about it. It’s more I’m tired of clearing the codes.

Exactly, it's hard to tell if there's something really worthy of looking at going on.

How was your experience switching out the cats? Also, do you know if theres a way to identify whether the cats are OEM or aftermarket? I recently bought an 04' v8 with P0420 & P0430 and am trying to identify whether an exhaust leak, bad downstream sensor or if the cats really are bad.

There's a reason O.E. converters (and aftermarket ones with sufficient precious metals) are like five to 10 times the price of the cheap ones. Looking on Rock Auto, I'm curious if the $1,000+ aftermarket manifold/converters match or come close to originals.

I too am experiencing 420 and 430 as of two months now but I did in fact have exhaust leaks at the connection point. These are "catalyst below threshold" fault codes, meaning there's excessive oxygen present past the cats, and the last O2 sensor is picking it up. The upstream o2 sensors don't care about the cats as they're technically AFR (air fuel ratio) sensors and don't throw this code.

In my case, I did fix the leaky exhaust, then reset the codes, and they're were gone for few days and now they're returned so i need to figure out how fresh air is getting introduced into the exhaust system. I'll do a smoke test this weekend to see if I can find the leak. I used all new hardware and donut gaskets for this project last weekend so I'm really annoyed at these two codes!

I have DT shorty headers + magnaflow California cats and no codes for the last six years. Aftermarket cats are not as good as OEM when it comes to longevity but they do the job just fine if your engine isn't dumping excessive fuel out of the cylinders and into the cats. Unburned fuel burns decreases the lifespan of cats or running too lean does the same thing.

Here's my exhaust thread in case you're curious Exhaust refresh - DT shortys + Magnaflow cross pipe