I need a catalytic converter for my 2000 HX civic.
 

Hello, I bought a 2000 Civic HX that has an aftermarket header installed without a cat and it throws a code for secondary O2 sensor. Best mpg I can get is 33-36mpg all highway.

What kind of catalytic converter should I get for the HX? I have been searching online for over a week and haven't found enough people who have actually changed their factory cat in an HX.

I am leaning toward just a cheap one but I want to make sure this car will lean burn properly with it.
Is this enough? Exhaust Manifold w Catalytic Converter Federal for Honda Civic Del Sol 1 6L | eBay
or do I need to get a better quality?

Take the 2nd O2 sensor and wrap a strip of sheet metal around it to make it read leaner.
That way you don't have to spend $150 or more just to find out the problem causing low fuel mileage is something else.
Throwing $150 parts at a car to troubleshoot a problem is what VW owners do.

You could also put a anti fouler on the downstream sensor, and see if that works. It does on Honda Insights.

I bought some spark plug anti foulers and tried that but the check engine light came back on. That was before I got a scanner so I going to different autozones to get codes read but that was a while ago...

I will try that again first.

I don't mind having to put a cat back on if that would fix it. I just don't want to waste money and there are very few resources on feedback of catalytic converters on the civic hx. The reviews are mixed and most people don't know what the hx is capable of.

Lean burn engine? I'd go to a junker and puck up a stock manifold and cat/downpipe...

When you cover the rear sensor the CEL can come back on. My friend that has done it on a 1999 sunfire and 1996 Tacoma says the car will throw a CEL about once every 4 to 6 weeks and his Tacoma gives a CEL about once or twice a year.
He has a scangauge in both vehicles so when the CEL comes on he turns it right back off.

He gutted the converter in the taco after it started to plug up from 250,000 miles of use, first he replaced the plugged up converter with a $400 dealer converter because he is fanatical about "keeping vehicles stock" then about a year later right about the time warrantee was up he failed Virginia state vehicle inspection because the converter catalyst was rattling around inside the housing. I was back in country the second time the converter failed and implemented the final solution, with my hammer drill and 3/4'' bit.

Both have duct sheet metal wrapped around the rear O2.

I don't like the idea of replacing the cat, especially with a cheapo unit that is sure to be junk.

The post-cat O2 sensor shouldn't affect fuel economy anyhow. It merely monitors cat efficiency, and isn't used to adjust fueling rates on the vehicle. The primary (upstream O2) sensor is used to fine-tune the A/F ratio.

Is it a P0420 code? How fast do you drive on the freeway?

An HX won't do lean burn when there is a engine diagnostic code thrown. And I think it might have had an exhaust manifold specially designed.

Try 2 anti-foulers on the lower oxygen sensor.

So do you think my best bet is to get an oem manifold? I am afraid to get a used one since they crack. And does it need to be an HX specific manifold/cat or can it be a LX or DX manifold. Since this car has an aftermarket header and no cat I don't which is the original and google images doesn't help alot.

I have those 2 anti-foulers and I may try them again.

The 1996-1998 Civic FSM shows the same exhaust manifold and catalyst for the D16y5 (HX) and D16Y7 engines. The D16Y7 was more common, and could be found in the DX, CX, and LX trims. The catalyst/exahust manifold that was different was on the D16Y8 engine, which was in the EX/Si trim. Get the OEM, and get the proper O2 sensor so you don't throw a CEL which will keep you out of lean burn.

HX Cat Converter
 

This one say's it's compatible w/2000 Civic HX. I have a 1998 HX and have used headers w/aftermarket Cat and never had problems with leanburn. I prefer the one like in this ebay ad. 45+mpg.

But you are running an Apexi AFC,so youare controling AFR in an unusual way. He is trying for stock functionality. This eBay item does not appear to have the downstream O2, or the heat cover for the catalyst. Seems dodgy to me. Just get the stock equipment, unless you wanna figure it out.

Apexi AFC
 

Yes, I run an Apexi AFC, and when I run the Apexi I get 55 mpg avg. When I ran the setup with headers and aftermarket cat I got 45 mpg avg, but I understand what you are saying about being leery of anything but stock setup on a leanburn system.

I am having a hard time finding a used factory manifold. All of the local junk yards don't have any and all the ones on ebay look like there from an EX.

What do you think about this one? Exhaust Manifold with Integrated Catalytic Converter Front Fits 96 00 Civic 1 6L | eBay

That one has the spots for both O2 sensors and looks more factory. it says refurb.

You wanna search car-part.com

After looking for a while I found a used manifold for $100 but I am afraid of it cracking next week or next year... Especially after reading all the reviews on amazon. So I ordered a new Dorman 674-439. I should have it install next weekend and will give an update. Thanks for all the input guys.

You probably know more about this than I do, but the reviews on Amazon were not exciting, and they mentioned unless you purchased it from the right place (not Amazon), you only receive a five-year warranty, not the lifetime guarantee Amazon states, and several people said aftermarket manifolds failed within a few years. I swear I once saw a hairline crack in my manifold by the upper oxygen sensor, but I took it to a welder and he did not see it, and he said it was square.

I tried JB Weld, which simply disappeared, but is only rated for 550 degrees. These products are supposed to be good for 2,000 - 2,500:
POR-15 Fire Seal 2000 FS2 - Free Shipping on Orders Over $99 at Summit Racing
Amazon.com: Blue Magic 18003 QuikSteel High Temperature Metal Repair Blister Card - 3 oz.: Automotive
Amazon.com: Blue Magic 18003TRI ThermoSteel High-Temp Metal Repair - 3 oz.: Automotive

I would personally prefer an OEM header welded by someone that knew what they were doing to an aftermarket one, but I welcome the opinions of more knowledgeable members.