Rep Power: 0

My wife has a '02 Civic LX 1.7L w/ 190k miles. She had a check engine light (bad catalytic converter). She drove with the CEL for a while because it was running fine but last week it started to sputter and lose power during acceleration (runs fine once up to speed) so we went ahead and replaced the cat. Now there is no CEL but it still sputters and loses power.
I'm not sure what would be causing this and not throwing a CEL?
A little more info:
The aftermarket cat we bought from rockauto came with the manifold gasket but not the one for the bottom. We went to O'reilys and the gasket they pulled up looked like a metal O-ring, whereas the old one looked like a tapered gasket that fits tight to the pipe (if that makes sense) They assured us the gasket they gave us was the right one so that's what we used. I don't know if that might be causing an exhaust leak and that might be causing the problem? How can I go about diagnosing and fixing this problem?

 
Rep Power: 518

Wrong gasket is wrong. Parts jockeys who have never turned a wrench are never wrong. LOL


They gave you a gasket like this


or this


but your car needs this?


If you know they tried to sell you the wrong part, you never should have taken it. Now you can't return it because it's used.

What's been done so far to correct this? Got more descriptions? Video? Misfire?

 
Rep Power: 0

Yes they gave me the one in the top pic. They told me even tho it looks different it would still work and that it would swell when tightened to form a seal. It was $3 so not a big deal that I can't return it. The old one does look like the one in the bottom pic. If I go to another parts store, what is this particular gasket called?

Anyways, I do plan on getting the right gasket but I'm thinking that is not the problem because a leak downstream of the o2 sensors shouldn't affect how the car runs right?

 
Rep Power: 518

Just take in the old one or take a picture of it. I'd call it a donut gasket, but it really doesn't matter what you call it if the kids at the parts store can't look up the right car on their parts cumpooter or the system is flat wrong. The kids working there usually have no freekin clue, they just look up some numbers and sell white boxes, never knowing or caring what's inside them. The cumpooter is never wrong.

If you want to find a real parts pro who actually knows WTF they are selling and knows their inventory as more than just numbers on white boxes, you'll probably have to find the parts stores that are not open on Sunday and charge higher prices.

The correct gasket from a Honda dealer should be about $21 (MSRP), and you can find it cheaper online

For the most part no, but it depends on what the actual problem is.
A leak can cause the downstream O2 sensor to read falsely and cause false codes, even though the leakage is downstream of the sensor. Seen it happen more than once.

If you have a clogged exhaust because the muffler is full of broken original catalytic converter guts, the exhaust leak might help performance by relieving some of the restriction
But I have no idea what the real problem is right now.



If this poor running problem is what ruined the original cat, it might ruin the new cat as well.