or you could read my bogs page, and see the on car cat test.
there are 7 ways to test the cat on car.
the most simple (well yours, is bad, if it wont come out , it's over 100k old, its a tune part, that.) you remove it and check the back pressure there.
drop header, rack back the exh manifold or just measure it.
Cat-Conv-testing
why-power-loss-index
keep in mind all posts here are guesses due to lack of testing.
only you can do the tests. (forget smog, first test, then fix then pass smog)
1: good motor (the EGR only needs to be closed, close it , defeat it ,drive.
still drive poorly, good it wasnt the EGR, end guessing.
2: compression. 170 or more warm/hot, WOT?
2a: sure the cat test. its was just a guess, here.... do that now.
bingo good motor, it can actually breath.
3: tuned up, new spark parts,? gaps .028" at sparks.?
4: fuel pressure.
