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Old 01-26-2018, 04:44 AM   #1
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So, I need new cats...

Quick backstory, since I'm new around here: I bought an '02 Boxster S with 116k on it from a mechanic on eBay last July. It drives like a dream, no regrets, even though it was throwing codes when the monitors reset after a week. And of course, the promised maintenance records were mysteriously "lost". But I love it, and want to bring her back to full health. I drive her into work on Fridays and do any weekend driving on her, weather permitting. (End of backstory.)

I've put a couple of thousand miles on her, so took her to the dealer to check on the codes, do a 120k mile tune up, and because the power steering was whining. So, the dealer has informed me that my catalytic converters are dead and they'd really like it if I gave them $8k for new ones. Yep. The codes (P0410, P1411, P0430, and P0420) seem to back up the diagnosis, leading me to consider my options. They're doing the tune up and fixing the power steering leak this week.

I intend replace the cats myself, but I have some questions.
1. New or used? Is there a deciding factor?

2. If new, opinions on the DEC option available at Pelican, or Softronic has a set from NHP, or ?

3. Is there anything else I should replace while I'm at it? O2 sensors? Full exhaust system?

4. Do most folks delete the rear cats?

5. I understand the fasteners can be rusted pretty thoroughly, and I've bookmarked some links in the forum for advice on how to loosen them, so I assume I should replace them? Do I need to order those separately if I get a used one?


My goal is to have a properly functioning car that will last many years, I'm not trying to squeeze every last hp out of her or get her to sound "better". That said, I'm not opposed to shiny upgrades where they make sense.

Thank you all for the years of advice I've found here, and for any insight you can share.

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Old 01-26-2018, 06:37 AM   #2
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$8K? C'mon.

https://www.buyautoparts.com/buynow/1998/Porsche/Boxster/Catalytic_Converter_CARB_Approved/45-34336_Z3?src=pla&pt_source=googleads&pt_medium=cpc&pt_campaign=(ROI)+Shopping+-+45-3+-+Year+Specific&pt_adgroup=Shopping+Ad+Group&gclid=EAIaIQobChMIusigy_r12AIVC4B-Ch0lGQR2EAQYBCABEgJPNfD_BwE
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Old 01-26-2018, 06:56 AM   #3
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I eliminated the rear cats years ago ('02 S) with bypass pipes, and have passed smog here in the Peoples Republik of Kalifornia several times, no issues.
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Old 01-26-2018, 07:41 AM   #4
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Originally Posted by navair View Post
I eliminated the rear cats years ago ('02 S) with bypass pipes, and have passed smog here in the Peoples Republik of Kalifornia several times, no issues.
I'm a newbie...

Is the cat setup different from that of a 98?

Did you notice any improvements borne by the absence of the rear cats?

In advance, thank you.
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Old 01-26-2018, 07:55 AM   #5
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The 97-99 USA cars have only the rear cats, and what is shown in the link above is generic weld in rear cats. On the 2000-2004, the USA cars have 2 sets of cats, and that first set that is integrated into the "headers" is the set that is monitored:



I have a 2000 S with around 137,000 miles, and ever since around 103,000 miles (when i got the car) I occasionally got the cat efficiency codes. With replacing some O2 sensors that were aging, etc... I was able to clear up these codes, although looking at the real time data using the Durametric diagnostic tool, I could see that the cats were nearing the end of their life. I replaced them with a pair of take off cats from a guy that installed race headers on his Boxster, and they only had about 20,000 miles on them, and so far they are working great.

If you got some used ones from a car that had lower miles, you could probably get years and years out of them. I replaced them myself, and while it was a hassle, it is doable by a "regular" person. I hit all the bolts with Kroil and let them soak, and didn't have any snap off.

I have replaced my 2nd cats with "test" pipes, and if you are changing your front cars, this is the perfect time to change those pipes. That 2nd set of cats isn't monitored so it doesn't throw any codes, and it does add a nice little enhancement to the sound, while not making your neighbors mad

I used new hardware that I got from Fastenal, I don't recall the threads, etc, but take some of the old hardware up there and they can match it up for you.

Last edited by steved0x; 01-26-2018 at 08:00 AM.
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Old 01-29-2018, 06:47 AM   #6
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Quote:
Originally Posted by steved0x View Post

If you got some used ones from a car that had lower miles, you could probably get years and years out of them. I replaced them myself, and while it was a hassle, it is doable by a "regular" person. I hit all the bolts with Kroil and let them soak, and didn't have any snap off.

I have replaced my 2nd cats with "test" pipes, and if you are changing your front cars, this is the perfect time to change those pipes. That 2nd set of cats isn't monitored so it doesn't throw any codes, and it does add a nice little enhancement to the sound, while not making your neighbors mad

I used new hardware that I got from Fastenal, I don't recall the threads, etc, but take some of the old hardware up there and they can match it up for you.
Thanks for the suggestions - I think I'll do the rear cat delete, and I'd never heard of Fastenal but will check them out.

I'm considering these headers, anyone used them?

Porsche 986 Boxster NHP 200 Cell Exhaust Headers
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Old 01-29-2018, 03:32 PM   #7
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I replaced my driver side CAT 2 years ago. Bought a new OEM unit for about $1600. Today, they list for about $4500 for both sides from ECS Tuning

The challenge in CA with aftermarket CATs is getting a shop to weld them into the exhaust system. Apparently, doing so can cause problems for repair shops. Probably not the case outside of CA, but who knows?
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Old 01-29-2018, 08:26 PM   #8
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So, I need new cats...

Quote:
Originally Posted by navair View Post
I eliminated the rear cats years ago ('02 S) with bypass pipes, and have passed smog here in the Peoples Republik of Kalifornia several times, no issues.
Interesting, how does a vehicle that is required by law, to have cats, pass smog without them? My b.s. alarm is shrieking at the moment.
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Old 01-30-2018, 03:52 AM   #9
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Quote:
Originally Posted by RobertKing View Post
Interesting, how does a vehicle that is required by law, to have cats, pass smog without them? My b.s. alarm is shrieking at the moment.
I believe rear cats aren't monitored and the smog shop didn't do a visual inspection as its required to do to discover the modification
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Old 01-30-2018, 04:01 AM   #10
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If you buy used cats from eBay, get them from a reputable seller. I bought one that was bad and the seller sent me another to replace it.
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Old 01-30-2018, 04:09 AM   #11
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How?

Simple. ONLY the front two CATs that are integrated into the header have O2 sensors monitoring them. The computer has no idea what is behind them. The second set of CATS are BEHIND the O2 sensors. You can delete the second set as long as the front set remains and nothing bad will happen. As a matter of fact, lots of great things happen. Just do it.
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Old 01-30-2018, 03:00 PM   #12
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Quote:
Originally Posted by Pepik View Post
Thanks for the suggestions - I think I'll do the rear cat delete, and I'd never heard of Fastenal but will check them out.

I'm considering these headers, anyone used them?

Porsche 986 Boxster NHP 200 Cell Exhaust Headers
I've been running those exact same headers on my 03 Box S for about a year along secondary cat delete pipes. They have been working great.
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Old 02-11-2018, 05:32 PM   #13
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I've been running those exact same headers on my 03 Box S for about a year along secondary cat delete pipes. They have been working great.
Thanks for the feedback, both you and everyone else on this thread.

I found elsewhere in the forum that if you upgrade the headers that you should reflash, and for some reason that kind of freaks me out. I think I'm going to go with used cats for now. If I'm wrong and I should really not worry too much about the reflashing, let me know.

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