Myth Busted: "Bad cat won't cause misfire"

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If it's choking off the airflow, of course it will cause misfire. You need the air/fuel mixture, spark and compression for the engine to operate.
 
Yup, see this exact set of symptoms with Mazda RX-8's all the time.

Usually it's a partially failing ignition coil that causes unburned fuel and oil to pollute the convertor, then all it takes is to get the convertor good and hot so that it ignites the mixture, which then destroys the convertor. That then causes the misfire code before too long, along with reduced convertor efficiency code.

Then, the exhaust smells terrible under acceleration.

But you can get awesome flames out the tailpipes, under just the right circumstances.

BC.
 
Originally Posted By: Kool1
Some people say the exhaust will smell bad and your eyes will burn without a cat. Does this really happen?


Those people are not too bright. It may burn if you are burning alcohol and running super rich. I have experienced that(methanol fueled drag cars), but never on a street car.
 
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Ive been running a Cat-less exhaust for the longest. Being that my car is over 25 years old, it only gets a safety test, no emissions.

Benefits are improved MPG and engine service life as well as more top end power (something that the 3.8 lacks, IMO). I put a Flowmaster on her and she sounds great (even though there is slight cabin drone).
It is more stinky, but I dont care, reminds me of the good ole days.
Ive hollowed out cats on several Panthers (Vics Gr.Marqs) back in the day, they always sounded funny to me.
 
Cats don't normally "kill themselves," there is most likely unburned fuel going into it that made it go bad in the first place ...
 
Originally Posted By: Bladecutter
Yup, see this exact set of symptoms with Mazda RX-8's all the time.

Usually it's a partially failing ignition coil that causes unburned fuel and oil to pollute the convertor, then all it takes is to get the convertor good and hot so that it ignites the mixture, which then destroys the convertor. That then causes the misfire code before too long, along with reduced convertor efficiency code.

Then, the exhaust smells terrible under acceleration.

But you can get awesome flames out the tailpipes, under just the right circumstances.

BC.


Like this?
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Originally Posted By: Nate1979
But how did the cat go bad in the first place?


Good question. She's not misfiring on her own, scan shows proper functions, and injectors are working properly. I can only assume is just reached the end of its life.
 
Of course a clogged exhaust will cause poor running on anything.
You're lucky that you can get by without a cat replacement where you live.
In many states, you would have had to fork out the bucks for new cats.
 
Not running cats on a vehicle is a choice I cannot endorse. As others have noted it is irresponsible and bad for our air quality in general.

Imagine if everyone decided to do the same? Wonder what would happen? Want government inspections to come back? I sure don't.

Funny that in our fleet we have not replaced any cats in my memory. Even at 500k miles our last truck sold still had it's originals in place and working correctly.

The last time I replaced one was in a 1976 Dodge van where the screen blew out and the pellets clogged the muffler. I can only wonder what you folks are doing to ruin a converter, they are pretty hard to kill IME.

"In the United States it is a violation of Section 203(a)(3)(A) of the 1990 Clean Air Act for a vehicle repair shop to remove a converter from a vehicle, or cause a converter to be removed from a vehicle, except in order to replace it with another converter.,[26] and Section 203(a)(3)(B) makes it illegal for any person to sell or to install any part that would bypass, defeat, or render inoperative any emission control system, device, or design element."

Yep, we should all just disregard the laws and do whatever we want...
 
My son's 4cyl Malibu had a coil go bad. This ended up ruining the cat and after a while he had no power. We finally changed it when he could not go over 20 mph.

Put on an after market one from Rock Auto. It fits but he gets a CEL. The cat and exhaust manifold are all one piece. Stupid GM.
 
Originally Posted By: SHOZ
My son's 4cyl Malibu had a coil go bad. This ended up ruining the cat and after a while he had no power. We finally changed it when he could not go over 20 mph.

Put on an after market one from Rock Auto. It fits but he gets a CEL. The cat and exhaust manifold are all one piece. Stupid GM.

install eBay headers and antifowlers and move on. In most states you can remove the precats, as long as the main cat is there and working.
 
Originally Posted By: SHOZ
My son's 4cyl Malibu had a coil go bad. This ended up ruining the cat and after a while he had no power. We finally changed it when he could not go over 20 mph.

Put on an after market one from Rock Auto. It fits but he gets a CEL. The cat and exhaust manifold are all one piece. Stupid GM.



Yeah stupid GM... GM and most other manufacturers...
 
'08 Accent I guess is part of the manifold. '10 Genesis Coupe (now without cats)
 
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I ran into this not too long ago with the rear cats on one of my vehicles. I ended up leaving the pre-cats in place and removing the post cats. No CEL, or odor difference. Slightly louder. I don't know which cats do what, but I still have 2 of 4 installed.

On a side note, on a previous Mazda, I replaced the cats twice on my own dime in 200k. I believe it was over $1k each.

I don't know what caused it, but in both vehicles the media essentially shattered and was coming out the tail pipe in honeycomb chunks and dust as I drove.
 
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