So after owning a 98 prelude and struggling with the same issue, I've finally found a fix. A friend of mine told me to get the magnaflow cat cuz it was a direct fit and wouldnt throw a cel. I did so, and replaced the o2 sensors (denso) and still threw a light. Go to
O2 Simulator, mini catalytic Converter cel fix and order the o2 simulator. I ordered the universal "mini-cat"...it's been about a month and the light hasnt come back on. Hope this was helpful. I also get 50 more miles per tank...good luck. hope it works out for you.