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Discussion Starter #1 (Edited)
Howdy, so I think the insides of my high flow cats might be loose or broken

I have been hearing rattling underneath the car for quite some time now (a couple years roughly), and its been getting worse lately, but whenever we have looked under the car we've never seen anything loose

It never occurred to me that it could possibly be the cats because i just assumed they last a really long time
(They're like 5yrs old, but I just ran across some guy on a forum saying they don't last that long?)

I just read that o2 sensors on OBD1 cars should be replaced like every 40-50k?....
So was thinking about putting new o2 sensors on here shortly....
(Ive never replaced them)
But maybe i should just remove the cats altogether?....
Can I just skip new o2s if i did that?
(I don't have to worry about emissions testing)

I cant remember if o2 sensor info was apart of the ECM tune?

And if i DID remove the cats would i need to do redo my ECM tune, or would cutting off the cats allow me to just ignore the o2s completely?

And here's a crazy question....
What if i just cut everything off and drove the car with open headers?

What exactly would happen if i just drove it like that?

Thanks
 

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O2s tell the engine how to adjust the fuel so it runs right - closed loop. It's feed back for if it is too rich or too lean.

Cats clean up the air. (exhaust). You still want the fueling correct, right?
 

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Discussion Starter #3
O2s tell the engine how to adjust the fuel so it runs right - closed loop. It's feed back for if it is too rich or too lean.

Cats clean up the air. (exhaust). You still want the fueling correct, right?
Yeah well for some reason i thought that the o2 sensors become way less necessary if you remove the cats

I thought i read that there's like 4 on these cars stock??....
But you can remove two, and then the remaining two are in separate places?

One in the engine on the passenger side, and the other IN the cat??

Then IF you remove the cats then you only need the one o2 sensor in the engine?

lmfao idk man im just trying to simplify as much as possible :ROFLMAO:
 

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On the 96s, there are 4 O2 sensors. One in front of each CAT, to do the closed loop thing. And one after each CAT, purely for OBDII diagnostics to tell if the cats have failed. A 94 won't have those, so you only have 2. One in front of each. Cats need the mixture right on or the will fail early. O2 make sure that mixture is right. If you don't have Cats, then it's not that critical and you'd be in open loop all the time. Mileage will be less. And you really wouldn't know if things are starting to get out of wack. They're not that expensive. 50K change interval is probably very conservative. I changed the ones in the 95 just a couple years ago. More so because of age. They had about 70-75k on them.
 

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Discussion Starter #5
On the 96s, there are 4 O2 sensors. One in front of each CAT, to do the closed loop thing. And one after each CAT, purely for OBDII diagnostics to tell if the cats have failed. A 94 won't have those, so you only have 2. One in front of each. Cats need the mixture right on or the will fail early. O2 make sure that mixture is right. If you don't have Cats, then it's not that critical and you'd be in open loop all the time. Mileage will be less. And you really wouldn't know if things are starting to get out of wack. They're not that expensive. 50K change interval is probably very conservative. I changed the ones in the 95 just a couple years ago. More so because of age. They had about 70-75k on them.
OK

96 has four o2s, and 94s have TWO....one in front of each cat....got it

So if my cats HAVE fallen apart on the inside this obviously means they're useless now, and i need to get them off right?

I don't want to spend any money on new cats if i can legally drive without them
 

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If they have fallen apart inside, then yeah, they aren't doing much. More worrisome would be if the honeycomb material rotates inside and then blocks off some of the flow. Best to clear out those chunks inside if you can get access.
Legally... they need to be on and functioning. That said. Would they know if they are not, depends on your state's inspection/emission policies. If they've worn out, do they have to be replaced, again that's the state's policy. Even here in NYC metro area, 25 and older get just a safety inspection now.
 

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The rattle might also be just the heat shield on them. Usually just tack welded on and they tend to rust at those points.
 

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Discussion Starter #8
The rattle might also be just the heat shield on them. Usually just tack welded on and they tend to rust at those points.
Ok ill check the heatshields

So if I remove the cats Im obviously going to need to get the ECM retuned right?
 

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So if I remove the cats Im obviously going to need to get the ECM retuned right?
Need? Too strong a word.
If you do not have catalytic converters, a few unnecessary protocols can be tuned out as part of a complete tune.
 

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Discussion Starter #10
Need? Too strong a word.
If you do not have catalytic converters, a few unnecessary protocols can be tuned out as part of a complete tune.
Ok so is that a yes or no lol

If i dont send the ECM off to get retuned for having no cats, and just drive it with the tune i have now once the cats are gone what exactly will happen?
 

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Discussion Starter #12
You'll be fine if you just remove the cats.
Ok, and what if I just cut everything off and drove it with open tri-y headers?

What exactly would happen if i drove it like that?

What are the specific pros and cons of open headers?
 

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If i dont send the ECM off to get retuned for having no cats, and just drive it with the tune i have now once the cats are gone what exactly will happen?
The pcm will waste fuel trying to protect catalytic converters that you got rid of.
Ok, and what if I just cut everything off and drove it with open tri-y headers?

What exactly would happen if i drove it like that?
You're gonna have to ask someone in your particular state, but It's not a good idea. Once you drive by a cop / government official / citizen with a bug up their ass, a process will be set in motion that will eventually force you to stop driving around with open headers.

It will not be worth the headaches your car will literally generate. Especially since a well-designed exhaust system will rob at most 8 horsepower from an open exhaust. Not an exhaustive pros & cons list. Sorry.

At this point I'm hoping you don't get pulled over for an exhaust that smells bad enough for someone to set another process in motion that will eventually force you to install some kind of catalytic converters on your car.

I would be happy to find out you got away with driving without catalytic converters AND an exhaust system - but the odds are against you in the long run.
 
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Discussion Starter #14
The pcm will waste fuel trying to protect catalytic converters that you got rid of.You're gonna have to ask someone in your particular state, but It's not a good idea. Once you drive by a cop / government official / citizen with a bug up their ass, a process will be set in motion that will eventually force you to stop driving around with open headers.

It will not be worth the headaches your car will literally generate. Especially since a well-designed exhaust system will rob at most 8 horsepower from an open exhaust. Not an exhaustive pros & cons list. Sorry.

At this point I'm hoping you don't get pulled over for an exhaust that smells bad enough for someone to set another process in motion that will eventually force you to install some kind of catalytic converters on your car.

I would be happy to find out you got away with driving without catalytic converters AND an exhaust system - but the odds are against you in the long run.
Right

Well im looking up the laws as we speak right now actually, and open headers definitely appear to be illegal here 😂:ROFLMAO:
 

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I drove my 63 with open headers 1 time and the cop I picked up 3 blocks short of the exhaust shop followed me the rest of the way there.

-Brian
 
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try smacking the cats with a deadblow.
you can hear if they rattle or sound hollow...

I got stopped for loud pipes in my S10 (sbc w/3" borla exhaust) but did not receive a ticket.
Drove my roady to the exhust shop after installing headers - sweating bullets the whole time lol.
 
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Discussion Starter #17 (Edited)
I got borlas on mine (with 2.5 inch pipes) and my exhaust sounds weak asf man

I should went flowmasters or spintechs, but if i remember correctly, the "features" on the borla page promised me "the deep mellow rumble that im looking for"

LMFAO

EDIT: Hopefully chopping the cats off will redeem the borla brothers!
:ROFLMAO: :ROFLMAO: :ROFLMAO: :ROFLMAO:
 

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Some of the borla systems aren't much quieter than straight pipes.
I'm sure deleting the cats will give it some more rumble...

The pcm will waste fuel trying to protect catalytic converters that you got rid of.
AFAIK it shouldn't waste any more fuel than if the converters were still in place.
 
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Some of the borla systems aren't much quieter than straight pipes.
I'm sure deleting the cats will give it some more rumble …
Borla's B- body exhaust system is notorious for being … understated.
AFAIK it shouldn't waste any more fuel than if the converters were still in place.
Unfortunately, the 'catalytic converter bit' adds fuel expressly to keep the catalytic converters from overheating.
If one lived in a state where one was lucky enough to be able to drive around without catalytic converters, but the pcm was not updated to reflect this, the pcm would continue to infer the existence of the catalytic converters (since it cannot detect their existence or temperature directly), continue making guesses at their temperature, and enriching the fuel mix / wasting gas every so often.
 
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