Hyundai Repair: Multiple misfire on all cylinders, fuel pressure gauge, hyndai accent

Question
i won a 99 hyndai accent with the 1.5 liter motor and it keeps on throwing the codes for multiple missfire on all cylinders as soon as you try to give it gas. I have changes fuel filter, replaced coil packs put new wires and plugs in.  it has 14200 miles on it and it looks like the factory cat is still on it.  Could the cat be plugged up or maybe a weak fuel pump.  What do you think i should do.

Answer
I'd suggest that the problem is most likely low fuel pressure.  I don't recommend replacing the fuel pump without diagnosis, however.  Low fuel pressure feels nearly exactly the same as a clogged catalytic converter, but the fuel pump is much more likely to cause misfire codes to set.  I'd recommend attaching a fuel pressure gauge and checking the fuel pressure.  If low, replace the fuel pump.