99 accord f23a4 manual transmission

Hello everyone. I was needing help identifying the correct cat for my 99 accord. It has a swapped f23a4 ulev vtec engine. I’ve done some research but cant be too sure which one it is. Thank you to all that reply. It is very much appreciated.

Was the original engine the f23a1? It’s almost the same as the f23a4 you have now. When I check online I don’t see any differentiation between cats available for different engines in a 1999 Accord. If you live in Cali or a state that uses their CARB specification, make sure it meets that.


Yes I live in Cali. And I have no idea what engine it had before. The guy I got it from didn’t tell me. But thanks for your input I appreciate it. Hoping to get it swapped because it’s currently not passing smog and I took it to a shop and they told me that’s what the issue is

That’s probably possible to determine from the car’s VIN number. Google VIN search, something to that effect. There may be an easy online method available. Also your local parts store may be able to do it using their parts computer system. Worse case, a dealership should be able to find that info without much trouble.

Another idea, ask your parts store to input your car’s vin as a prelude to a cat search. Might be informative.

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Open the hood, and you’ll find the emission sticker that reflects the engine that originally came in the car.



IIRC from years ago if doing a later model engine swap, all the emissions stuff has to match the engine year of the newer engine…
But unless they are popping the hood and checking the date codes and stuff on the engine I would think that the converter that matched the emission sticker that Tester showed for your car should be the correct one… Obviously if you swapped a Hellcat Hemi (yes I know) in it the Hellcat converter would not fit…

The folks more familliar with Cali emissions testing may know better but if the OBD2 scanner is plugged in, it will read the ECU’s ID so the cat many need to match the ECU.

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