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Discussion Starter #1 (Edited)
A lot of us have heard the dreaded CAT stories, and I’m wondering if it’s something that should warrant preventative measures.

My 2012 P4x (150k) seems to be fine, but I’d replace the cats early if I thought they may dust the engine?

Does anyone have any hard facts on this? Was it limited to earlier years? Too few occurrences to really worry about? Or something we should try and prevent?
 

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2021 P4X?

It’s generally accepted that when the CATs go they can take out the engine. Based on my understanding if you gut your secondary, non-monitored CATs, this risk drops dramatically. It’s also worth noting that typically (but not always) you’ll get a CEL before they catastrophically fail.

Some members say the dusting issue is BS. I say why risk it. I plan on gutting my secondaries at 100k and going from there. My 2011 had 140k on the original CATs when it was totaled and going strong.
 

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Discussion Starter #3
2021 P4X?

It’s generally accepted that when the CATs go they can take out the engine. Based on my understanding if you gut your secondary, non-monitored CATs, this risk drops dramatically. It’s also worth noting that typically (but not always) you’ll get a CEL before they catastrophically fail.

Some members say the dusting issue is BS. I say why risk it. I plan on gutting my secondaries at 100k and going from there. My 2011 had 140k on the original CATs when it was totaled and going strong.
Ha, yes. My brand new 2021.
(Meant 2012)
 

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Chances are small that you will trash your engine, but it's a possibility. Some have had cat issues in as few as 80k, others have gone 200k+ with no issue.

In my opinion, I wouldn't mess with it until you get some check engine codes.
 

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Please don't gut your secondaries.

This is another old wives tale and in this instance one that all of us are going to smell and breathe because people are acting on conclusions that don't follow from reasonable premises.

Modern catalytic converters are generally made to last the life of a car though most don't. Things that kill them are severe impact, repeated impacts, and likely the most common one, engines operating outside of parameters. Severe heat and the wrong substances flowing through from things like improper A/F ratio, lean/rich condition, misfiring cylinders, chemical additives, poorly maintained PCV system, etc, can destroy or render the cat substrate & coatings ineffective.

This is when your car throws a P0420 or 0430 code. That code is derived from comparing the upstream and downstream O2 sensor readings and is triggered when the delta between them falls too low. To fix some incorrect information from another post, your downstream O2 sensor serves no purpose except to let you know when your cat/s (in our trucks only the primaries are monitored) go bad. The upstream sensor is critical to monitoring cat health(another post made a claim this was its only job), but serves a more important role of sending exhaust gas O2 readings to the ECM that help it adjust AF ratio, valve timing, and the host of crazy things a modern car does to run smoothly & efficiently.

What does all this mean?

Your best preventive maintenance is not replacing a cat or deleting your secondaries, but rather keeping your engine healthy, ensuring your O2 sensors function correctly, immediately addressing CEL's, and taking the time to inspect the substrate if you get a P0420 or 0430 code.

The earth is round, Biden won the election, and you will be significantly better off installing an oil catch-can and changing plugs & O2 sensors than replacing healthy cats with aftermarket junk as a PM move op.
 

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Please don't gut your secondaries.

This is another old wives tale and in this instance one that all of us are going to smell and breathe because people are acting on conclusions that don't follow from reasonable premises.

Modern catalytic converters are generally made to last the life of a car though most don't. Things that kill them are severe impact, repeated impacts, and likely the most common one, engines operating outside of parameters. Severe heat and the wrong substances flowing through from things like improper A/F ratio, lean/rich condition, misfiring cylinders, chemical additives, poorly maintained PCV system, etc, can destroy or render the cat substrate & coatings ineffective.

This is when your car throws a P0420 or 0430 code. That code is derived from comparing the upstream and downstream O2 sensor readings and is triggered when the delta between them falls too low. To fix some incorrect information from another post, your downstream O2 sensor serves no purpose except to let you know when your cat/s (in our trucks only the primaries are monitored) go bad. The upstream sensor is critical to monitoring cat health(another post made a claim this was its only job), but serves a more important role of sending exhaust gas O2 readings to the ECM that help it adjust AF ratio, valve timing, and the host of crazy things a modern car does to run smoothly & efficiently.

What does all this mean?

Your best preventive maintenance is not replacing a cat or deleting your secondaries, but rather keeping your engine healthy, ensuring your O2 sensors function correctly, immediately addressing CEL's, and taking the time to inspect the substrate if you get a P0420 or 0430 code.

The earth is round, Biden won the election, and you will be significantly better off installing an oil catch-can and changing plugs & O2 sensors than replacing healthy cats with aftermarket junk as a PM move op.
Yep.
Call me radical, but I'm of the opinion that "tread lightly" principles that most of us on this forum ascribe to (or at least claim to) also apply to the air.
Proper maintenance and fixing things properly when they break are pretty good insurance. A catch can is pretty easy to pick up and install too.
 

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Please don't gut your secondaries.

This is another old wives tale and in this instance one that all of us are going to smell and breathe because people are acting on conclusions that don't follow from reasonable premises.

Modern catalytic converters are generally made to last the life of a car though most don't. Things that kill them are severe impact, repeated impacts, and likely the most common one, engines operating outside of parameters. Severe heat and the wrong substances flowing through from things like improper A/F ratio, lean/rich condition, misfiring cylinders, chemical additives, poorly maintained PCV system, etc, can destroy or render the cat substrate & coatings ineffective.

This is when your car throws a P0420 or 0430 code. That code is derived from comparing the upstream and downstream O2 sensor readings and is triggered when the delta between them falls too low. To fix some incorrect information from another post, your downstream O2 sensor serves no purpose except to let you know when your cat/s (in our trucks only the primaries are monitored) go bad. The upstream sensor is critical to monitoring cat health(another post made a claim this was its only job), but serves a more important role of sending exhaust gas O2 readings to the ECM that help it adjust AF ratio, valve timing, and the host of crazy things a modern car does to run smoothly & efficiently.

What does all this mean?

Your best preventive maintenance is not replacing a cat or deleting your secondaries, but rather keeping your engine healthy, ensuring your O2 sensors function correctly, immediately addressing CEL's, and taking the time to inspect the substrate if you get a P0420 or 0430 code.

The earth is round, Biden won the election, and you will be significantly better off installing an oil catch-can and changing plugs & O2 sensors than replacing healthy cats with aftermarket junk as a PM move op.
COMEDY!
 

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Your emissions output meets EPA standards after the first cat - proof being its the only monitored cat and the EPA wouldn't allow it to be sold in the first place if the monitored emission systems didn't achieve EPA requirements. Nissan themselves don't call the secondary a cat they call it a pipe - and its not covered under the 80K emissions warranty. Why its there I am unsure - perhaps somewhere like California actually puts a sniffer in the pipe as well as check OBD and maybe it helps a little?

Before you start lecturing me on emissions get China to cut there emissions and I might pay some attention. Until then as the old saying goes - were just @#%% in the wind.

Gutting your secondary is a possible mitigation of an imploding primary cat but not a for sure. I generally agree however that the factory cats are much better than the aftermarket, and a catch can surely won't hurt.
 

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I am currently tearing down my old motor that was hurt by disintegrated cats. So far have found about 5 or 6 noticeable scratches on cylinder walls just enough to feel with a fingernail. But they look like they are light enough to smooth out with a cylinder hone and the motor be re-buildable. I will know better once the pistons are out of the cylinders.
 

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If you can feel the scratches you can't clean them up with a hone.
You are going to have to have them professionally measured and see if they can be cleaned up by boring oversized.
 

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I think the majority of cat destroying engine situations are related to ignored/covered check engine lights. My first Xterra had a misfire for months before I discovered the exhaust was restricted thanks to the previous owner covering the check engine light. The primary cat was falling apart and totally plugged up the secondary. I lucked out; but the exact same situation could have resulted in cat material in the combustion chamber.

So my thinking is gutted secondarys probably does reduce the risk; but exhaust valve adjustment and not ignoring trouble codes is even better.


Nissan v8 Titans (2003?-2008?) have the cat even closer to the engine and the issue is legendary. I wish Nissan (and everyone) would just put the cats further down the exhaust; which would also make them more accessible.
 

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I think the majority of cat destroying engine situations are related to ignored/covered check engine lights. My first Xterra had a misfire for months before I discovered the exhaust was restricted thanks to the previous owner covering the check engine light. The primary cat was falling apart and totally plugged up the secondary. I lucked out; but the exact same situation could have resulted in cat material in the combustion chamber.

So my thinking is gutted secondarys probably does reduce the risk; but exhaust valve adjustment and not ignoring trouble codes is even better.


Nissan v8 Titans (2003?-2008?) have the cat even closer to the engine and the issue is legendary. I wish Nissan (and everyone) would just put the cats further down the exhaust; which would also make them more accessible.
I ran mine with codes for a couple hundred miles - no issues. However not trying to be alarmist but I think it was J Sexton? that got like 5 miles from code to blown. Someone else here had no codes - the cats let go, got sucked into the engine, and that was it. Its unlikely but it has happened, so people need to decide themselves.

The trend for cats close to the manifold is to keep them super hot so they last longer. The new Titan V8's actually have the CAT integrated with the exhaust manifold - to remove the gasket and make heat transfer even better I guess. So when they go you get to change the whole exhaust manifold. Yea what fun / sarc.
 

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Discussion Starter #14
Well. I guess there's not really a hard answer to this.

I'd really love to just replace the primaries and not have to ever think about it again, but something about it just feels unnecessary. My X isn't my DD, but I use it for family camping trips, so the thought of being 300 miles from home with my wife and daughter and it kicking a CEL for the cats doesn't sound great.
 
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