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Can't pass smog with brand new engine!

Good for you! I have a 4AFE equipped Corolla and have been battling the same problem, high HC’s making it not pass Calif emissions. There’s a thread you can probably find using the search feature here on all that, if you run into this problem again. I can always get mine to pass, but barely. A combination of retarding the ignition timing, making sure the engine is properly heated to operating temp, new spark plugs, cap, rotor, & wires usually does the trick. Sometimes I have to use an injector cleaner too.

I expect my problem is different than yours, since you had a brand new cat. My cat is the same age as the car, 24 years. But your post makes me wonder if I might have a little bit of a fuel pressure problem, so I’ll check that out next time emissions testing is up.

Edit: One thing that seems to help for HC is to use the type of NGK plug called “V-Groove” , or something to that effect. Yields a little bit more robust spark I guess.

Well, this is at least one example of emissions testing doing what it is supposed to do. Now your car runs cleaner.

It’s kind of nice to see a government program achieve its intended effect, even if it was a hassle.

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It’s sort of curious why replacing the fuel pressure regulator would solve an overly high HC problem to the extent it did. I mean with no diagnostic codes. If the fuel pressure were a little high, but still within the specification range, the injectors might pulse a little more gas per injection, but the upstream O2 sensor’s reading would allow the engine computer to compensate for that, which would just decrease the injection pulse time. You’d think anyway… I’m guessing there’s something more than just the fuel pressure involved. But the OP got some luck and replacing the fuel pressure regulator fixed whatever that problem was.