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.