Symptoms of clogged cats?

[Alpine 7even]

Hey guys,

Can I get some collective info on what symptoms my 97 m62 would have if the cats were clogged or are on their way to being clogged? Also what potential codes can I expect to see?

I have acouple symptoms and a code right now, but before I mention them I'd like to see if any of what you guys say matches what I'm dealing with. Thanks guys!

[sigtwenty]

P0420/0430 are the only two cat codes our cars will probably ever see on the v8 models. Those are triggered by the rear oxygen sensors.

Mpg at or below 15.
Sluggish on cold startup
Rattle noises
Lack of power
Odd rumbles when driving in severe cases.
May cause improper shifting. Erratic downshift when coasting or slowing down.
May cause the cars overdrive gear not to engage at speeds over 45 unless you shift to sport mode then back to adaptive.


My 98 has bad cats and all the above is my current situation except for the over drive.
My 96 did have the over drive problem solved with new cats, but didnt throw a code, didnt have sluggish cold startup, or a lack of power.

[Erroneous]

Are you hearing a rattle?

[Mayorchuck]

I never did get codes with mine. Each time there was a noticeable lack of power especially when trying to accelerate quickly. My noise was a combo rattle/knock that was easy to isolate to the cat.

[Erroneous]

I never did get codes with mine. Each time there was a noticeable lack of power especially when trying to accelerate quickly. My noise was a combo rattle/knock that was easy to isolate to the cat.

Yeah exactly that's why i asked if there was a rattle, its almost always the cat when a noticeable rattle is present.

[Alpine 7even]

Did you guys ever have a pulsing vibration if while in park you took the revs up to about 2000-2500? I also got a knock sensor bank1 code no other codes though. I drove her around four about 4 hours today and had to sit in traffic on the freeway and she seemed to take off. No check engine light since clearing it with inpa. No noticeable rattle either.

[Erroneous]

Did you guys ever have a pulsing vibration if while in park you took the revs up to about 2000-2500? I also got a knock sensor bank1 code no other codes though. I drove her around four about 4 hours today and had to sit in traffic on the freeway and she seemed to take off.

Pulsing vibration as in idle pulsing?

[sigtwenty]

It can cause backfires, misfires and all kinds of stuff because the back pressure is messed up

Ghetto test

Bang the hell outta the cats. See if car runs and drives better. Even if a small change. Listen especially for rattling noises.

[Zedbimmer]

CATS will give you an issue taking off especially if they have reached a point to where they are throwing codes and rattling.

[Alpine 7even]

Pulsing vibration as in idle pulsing?

The idle is perfect and non fluctuating at 720 rpm. It's when I put my gas pedal and take the rpm up to 2000 - 2500. Anything after that and it smooths out nicely. Because its than pushing the exhaust has pass a potentially clogged cat (my assumption of course)

[Erroneous]

The idle is perfect and non fluctuating at 720 rpm. It's when I put my gas pedal and take the rpm up to 2000 - 2500. Anything after that and it smooths out nicely. Because its than pushing the exhaust has pass a potentially clogged cat (my assumption of course)

Ok so its not a timing issue, only other thing outside of the cat could be a misfire or clogged injector.

[Slimm]

If the cats are original, the exhaust kinda smells like gun powder.

[doc4car]

A vehicle with a clogged cat usually takes off god when cold but get worse as it warms up.

[Only1Balto]

This is good info

[Slimm]

A vehicle with a clogged cat usually takes off god when cold but get worse as it warms up.

+1. Loses power as it warms up.

[Binjammin]

The idle is perfect and non fluctuating at 720 rpm. It's when I put my gas pedal and take the rpm up to 2000 - 2500. Anything after that and it smooths out nicely. Because its than pushing the exhaust has pass a potentially clogged cat (my assumption of course)

Cats don't "clog". If you have an issue where you're not flowing through a catalyst housing it's because the catalyst ceramic has broken and plugged the cat. The honeycombs of the cat do not become clogged with things like soot.

The more the exhaust is blocked from anything, including broken cat ceramics, the more the car will be impacted in performance with rpm. A cat that has broken and plugged the exhaust stream will sometimes idle fine, but when you give it more rpm it falls flat and almost stalls. It almost feels like ASC kicking in. If you have a cat broken enough to affect your idle, it's highly unlikely that your car will run better with rpm increasing, especially smoothing out. That's the sort of thing that works once, like... let's say your cat has broken... the ceramic is rattling around, and partially blocking the outlet and it affects idle by drastically increasing backpressure in the system. You give it rpm and the piece blocking the outlet breaks up and spits out the muffler... it won't go back to affecting the idle again, because the piece is gone. I've seen cats break up where they block the outlet under rpm, but that doesn't affect idle.

Other symptoms are really stinky exhaust, like unburnt fuel. You can sometimes hear a rattle. You can scope the pre and post car o2 sensors. Post cat should be a steady stream, having been cleaned by the catalyst. If it's not, you may have a cat that's broken up and been spit out.

[Alpine 7even]

Great info!! What should the o2 and lambdas look like?

[shenofjo]

I been having a bunch of what seems to be unrelated symptoms but looking at this, I'm thinking it's my catalytic converter starting to fail.
First symptom: light rattle noise that comes and goes while stopped in drive but not in idle or park.
Second: when first driving the car while cold, it feels very torquey and powerful, but it seems to level off when it warms up. (Thought it may be the trans software to stay at higher revs in cold start to warm up faster)
third: when I redline through several gears I get misfires in multiple cylinders, catalyst damaging codes. (My mechanic thought I might have hit the rev limit)
Fourth: fuel smell when it is in cold weather but no obvious fuel leaks.
Fifth: I get poor fuel economy from 15-17. No matter how I cruise it. Thought it may be the supercharger and 3.15 diff.

one thing I read from another thread was the violent shake between shifts may cause a loose battery connection to cause misfires as well. Will rule that out when I get to check the connections tomorrow. Otherwise, what is a good way to test the cats? Any way to unclog it?

[Trasportador]

Op, remove the pre cat sensors from both banks, but leave them connected. Let the car warm up, and then increase rpms, see what you get.

This will answer your catalyst question

[daytonatrbo]

I been having a bunch of what seems to be unrelated symptoms but looking at this, I'm thinking it's my catalytic converter starting to fail.
First symptom: light rattle noise that comes and goes while stopped in drive but not in idle or park.
Second: when first driving the car while cold, it feels very torquey and powerful, but it seems to level off when it warms up. (Thought it may be the trans software to stay at higher revs in cold start to warm up faster)
third: when I redline through several gears I get misfires in multiple cylinders and catalytic converter codes. (My mechanic thought I might have hit the rev limit)
Fourth: fuel smell when it is in cold weather but no obvious fuel leaks.
Fifth: I get poor fuel economy from 15-17. No matter how I cruise it. Thought it may be the supercharger and 3.15 diff.

one thing I read from another thread was the violent shake between shifts may cause a loose battery connection to cause misfires as well. Will rule that out when I get to check the connections tomorrow. Otherwise, what is a good way to test the cats? Any way to unclog it?

If you have a supercharger and you have WOT misfires and lack of power when warm, it sounds like you are running dangerously lean. What tune are you running?

[shenofjo]

It's a dinan engine and trans software, I wouldn't say major power loss, just not as strong as when first starting. Would running lean cause the bad fuel economy?

[shenofjo]

Just a follow up:
First symptom: light rattle noise that comes and goes while stopped in drive but not in idle or park.
Second: when first driving the car while cold, it feels very torquey and powerful, but it seems to level off when it warms up. (Thought it may be the trans software to stay at higher revs in cold start to warm up faster)
third: when I redline through several gears I get misfires in multiple cylinders, catalystdamaging codes. (My mechanic thought I might have hit the rev limit)
Fourth: fuel smell when it is in cold weather but no obvious fuel leaks.
Fifth: I get poor fuel economy from 15-17. No matter how I cruise it. Thought it may be the supercharger and 3.15 diff.


The misfires were frequent when revving up the RPMs due to the high ktemp that resulted from a failed electrical thermostat. upon replacing the thermostat, it decreased operating temp to 98-102 has stopped misfires all together for 1.5 years until today. The fuel smell came from a slightly loose fuel hose clamp that I saw oozing fuel on the engine block when cold and tightened it up and never came back. I am now back to having 1 misfire event on cylinder 4 when I revved it out and wonder what it could be. I was using fuel injector cleaner religiously where i dump ~2 oz in per tank, but been lazy the last 2 fill ups and wonder if that could be it.

Symptom 1 and 2 are still there, but with symptom 2 I just downshift to be in 3-4k rpm and off i go! my gtech shows that with 4500lb setting and accelerating in low gears put me at 280RWHP + wind resistance and rolling resistance. Where should I go from here now that I got this misfire again? History of misfire on cylinder 3, 4, and yesterday on 4, lower indicated gtech HP and low rattle and loss of low end torque a sign of clogged cat?

[igmas]

Does the misfire happen when you rev it in N and P or does it rev normally?

I have the misfire on the 1,2,3,4 today these happened at low rpms 1000-2000. Before that mostly 1 and 2 misfired at high rpms 3500+
When I drive it around the car struggles to rev.
But in N and P the car revs fine.

[jazigk]

I just had cat issues and had mine replace with aftermarket 200cell's ($220aud both cats and $140aud labour).

My car would only miss up high, 4K rpm or up, driving. Never missed while free revving.

[igmas]

So the right back cat was clogged and the front cat was blown out the material was bouncing against against the back cat.