Delete 2nd Cats & Pass Inspection?

DeepFriedAsparagus

New Member
Apr 12, 2020
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Portland, Oregon
Hello,

I own a 2003 3.8l V6 Mustang Convertible (5spd manual), all stock. Next week, I am going to be building a custom dual exhaust for it (either divorced or H-pipe; can't decide). While I was looking underneath to make measurements, I saw the second set of cats (long ones with the flat plates on them), and wondered how much smog it actually removes. In my area (Portland, OR), we test for emissions, so this is important. The Oregon DEQ tests by inserting a plug into the cars computer (Is that called a sniffer? Sorry for my limited vocab). I did a little bit of research, and saw multiple 99-04 V6 owners say that they just removed the 2nd cats, reinstalled the O2 sensors (using a bung, I assume), and no check engine light came on. I was curious to see if any of y'all have had issues with your engine light after deleting the secondaries.

Thanks
 
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Noobz347

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You will not pass an emissions inspection with the 2nd set of cats in a 2-stage system, removed. What might be possible if there is no visual inspection, is to replace all four converters with 3-way converters.

Commieformia for instance, requires that there be 4 converters if the car was manufactured with 4 converters.

Furthermore, simply removing the 2nd set of converters gains you virtually nothing unless they are clogged.
 
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acsny97

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Sep 5, 2016
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It's hit or miss, depends on your inspector. I had a 2002 v6 with the Pypes dual exhaust, X pipe and 2 high flow cats instead of 4. I would sometimes throw codes when it was cold out but otherwise it was fine. The second set of cats are called precats and they simply remove the "extra" smog that your car might produce before when the main cats are cold. As long as Oregon is not a CARB state you should be fine but keep your old cats and midpipe just in case. Personally if it's a custom job I would just adapt the stock midpipe to be an H instead of a Y. Or just get a dual catback from the Y pipe. Coming from someone who has to deal with CARB laws, if your state tests for emissions it's always easier to just be emissions compliant. You don't really gain all that much performance wise removing the cats.

The plug into the computer is the OBDII test and is not a sniffer. Just checks for codes. Sniffers are devices that measure the actual emissions from your tailpipes and I have no experience with how easy or difficult those are to pass.
 

nickyb

WAIT,you now have a pair?
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Apr 3, 2009
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I know the limits are higher for my 93 but I got it with two cats removed(12 years ago) and passed
sniffer test in Nevada every year,even after putting 109,000 more miles on her.
IMG_20200417_165357_hdr.jpg
 
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DeepFriedAsparagus

New Member
Apr 12, 2020
6
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1
Portland, Oregon
You will not pass an emissions inspection with the 2nd set of cats in a 2-stage system, removed. What might be possible if there is no visual inspection, is to replace all four converters with 3-way converters.

Commieformia for instance, requires that there be 4 converters if the car was manufactured with 4 converters.

Furthermore, simply removing the 2nd set of converters gains you virtually nothing unless they are clogged.
Thanks for the feedback. I'm glad I don't live in the state where everything will give you cancer ;)
 

DeepFriedAsparagus

New Member
Apr 12, 2020
6
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1
Portland, Oregon
It's hit or miss, depends on your inspector. I had a 2002 v6 with the Pypes dual exhaust, X pipe and 2 high flow cats instead of 4. I would sometimes throw codes when it was cold out but otherwise it was fine. The second set of cats are called precats and they simply remove the "extra" smog that your car might produce before when the main cats are cold. As long as Oregon is not a CARB state you should be fine but keep your old cats and midpipe just in case. Personally if it's a custom job I would just adapt the stock midpipe to be an H instead of a Y. Or just get a dual catback from the Y pipe. Coming from someone who has to deal with CARB laws, if your state tests for emissions it's always easier to just be emissions compliant. You don't really gain all that much performance wise removing the cats.

The plug into the computer is the OBDII test and is not a sniffer. Just checks for codes. Sniffers are devices that measure the actual emissions from your tailpipes and I have no experience with how easy or difficult those are to pass.

Thanks for sharing your experience and going over their functionality. I've never seen them do anything besides plug in the OBDII reader, so fingers crossed I can remove the secondary without the light coming on. H-pipe is a good idea. I was going to do true dual, but I have a friend who MIG welds, and he said he might be able to fab an "H" for me. I mainly wanted to remove the secondaries for sound purposes (getting a deeper note), so no performance gain is not going to bother me.
 

DeepFriedAsparagus

New Member
Apr 12, 2020
6
0
1
Portland, Oregon
I know the limits are higher for my 93 but I got it with two cats removed(12 years ago) and passed
sniffer test in Nevada every year,even after putting 109,000 more miles on her.
IMG_20200417_165357_hdr.jpg
Sweet fox! I really like the long tips. I was planning to get something similar for mine. That's neat how long you've been able to pass without 2 of them. Gives me hope.
 

nickyb

WAIT,you now have a pair?
10 Year Member
Apr 3, 2009
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Thanks, I picked up an exhaust from letgo.Bbk shorties , x pipe , all loudmouth cat back for $160 bucks.killer deal I know.I only used cat back as I've got longtubes and old school h pipe.
 

stormsedge

Active Member
Jun 17, 2018
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You won't pass the emissions visual for sure. There really isn't any performance gain (at your current level of modification) worth disabling the emissions system. Save yourself some pain and keep it.