How can you tell if a catalytic converter is bad?

[GeoffM]

1. Any really easy way to tell?
2. Do they "expire"? See number 4
3. I recently fixed my friends exhaust. I went to the local machine shop and saw a bunch of exhaust bits, flanges included.
4. I want to skip the eventuallity that my cat will fail. I want to take it off and store in it my garage until I sell/need it. Will it go bad?
5. Any unforseen bad things that might happen?

Michigan doesn't have emmisions so I'll be good. I may just be getting exicted after my first sucessful weld, but I also think I might get better mileage.

[deevergote]

Replace it, don't delete it. With a deleted cat, your car will sound and smell terrible. Plus, if you develop an exhaust leak, you may be spewing a good deal of toxic fumes into the cabin. Plus, regardless of emission laws, you're still polluting the air! There was a time where no state had emission laws... but those that developed poor air quality adopted them. That poor air quality is because people didn't care about emissions!


Anyway, to tell if it is bad... if it is REALLY bad, as in clogged, then your car will run poorly. If it is blown out, the insides will be broken to bits. Of course, it has to be removed to learn this. Really, the only way to tell is to remove it.
If preventative maintenance is your goal, remove it, and replace it with a quality unit. Even the OEM cat is very free flowing, so you don't need anything "performance". Just get a good replacement of the proper diameter.

[GeoffM]

With a deleted cat, your car will sound and smell terrible. ... regardless of emission laws, you're still polluting the air!

Is it really that bad?

There isn't any problem with it, like I said I got really excited about welding and just wanted to take it off. If there's a leak after the cat, won't it still smell bad? My friends broke right after the cat and the exhaust kept smelling up his car.

[deevergote]

Yeah, it really is that bad. The only people I've ever known to LIKE a deleted (or hollowed... which is even worse) cat are highschool ricers that think a stinky, raspy car is cool.

[GeoffM]

I was talking about a straight through. How much different is the sound? I wasn't planning on taking off the muffler.

[deevergote]

It sounds like shit. Deleted or hollowed, doesn't matter.

Deleted will give you MAYBE 1-2hp... hollowed will cost you power.

My friend runs a test pipe at the track. Basically, straight through. It sounds horrible, smells horrible... and it's illegal, at least in NJ. He bolts it on for the track, and removes it that night (or the next day), and puts his cat back in.

[GeoffM]

I think it's federally illegal, so everywhere. If it's that bad I'll just leave it till it goes. 1-2 hp isn't worth it.

[bcjammerx]

go get a cheapo infrared temp gun...run the car to warm up temps (fan comes on)

check the temp of the pipe right before the cat, check the temp on the cat, and check a couple inches after the cat

the cat should be the hottest part of the exhaust

it should be SIGNIFICANTLY hotter...cops can do this easy test to see if you gutted it

you could plug in a second o2 sensor afte the cat that should pick up nothing

[GeoffM]

go get a cheapo infrared temp gun...run the car to warm up temps (fan comes on)

check the temp of the pipe right before the cat, check the temp on the cat, and check a couple inches after the cat

the cat should be the hottest part of the exhaust

it should be SIGNIFICANTLY hotter...cops can do this easy test to see if you gutted it

you could plug in a second o2 sensor afte the cat that should pick up nothing

I could claim that I didn't know it was gutted. But the straight through pipe, that's just a pipe. I'd like to meet the cop who will kneel on the ground to examine my exhaust. I'd almost applaud them for writing me a ticket.

[deevergote]

They have little wands with mirrors on them, made specifically to check under a car.

And ignorance is never a valid defence. You are expected to know every detail of your car, and to keep it legal at all times.

Of course, if you gut it, it'll create an area for severe turbulence, which creates one hell of a restriction. You'll lose power that way.



There are straight pipes on ebay that are made to look like cats... but even if you fool a cop, you still have an obnoxious, smelly, potentially dangerous car.

[red07frontier]

Easiest way to tell of you cat is bad is to listen while your driving and see if you hear your exhaust rattling. 9 out of 10 times when your cat is bad it will break apart. ( the cat is a bunch of honeycomb material inside )
what happens is when your car runs badly unburnt fuel will enter the cat and create a hot spot inside and melt the honeycomb and it will break apart. You will hear a obvious rattle when this happens. If it continues then it all breaks apart and goes down into the muffler. Then the muffler is full of cat and the muffler will rattle like it has rocks in it. The other thing that can happen is they plug up but it very rarely happens on hondas and you know when it does.

Now I agree that you should not remove it but it does help with flow by increasing pipe size. If you choose to remove it then put a small resonater in place.

I personally haven't seen any that (smelled) worse without a cat. It's gonna smell like exhaust, not much difference. The smell is the fuel and is mostly poorly tuned cars and carbed cars and trucks.

Long story short, if you don't hear any rattling and the car runs fine leave the cat alone unless you get a larger one for more power and flow.
( match to exhaust, I.E. 2.5" exhaust then 2.5" cat)

[red07frontier]

Also make sure to match the cat to your emissions state.
Cali requires at least a 3 stage 50 state legal. Others are fine with a 2 stage 49 state legal.

Technically a cat has no moving parts so they don't expire unless outside influences affect them.

You can also smack the cat with your fist when it's cold to see if you hear it broken apart inside

[GeoffM]

You can also smack the cat with your fist when it's cold to see if you hear it broken apart inside

I almost want to add this to my signature. But it's getting kinda big. What's a resonator?

[deevergote]

A resonator is like a small muffler that goes in the middle of the exhaust piping.

[red07frontier]

Ever seen those red cherry bomb mufflers? That's a resonator. You have one on your accord in between the cat and muffler.