1991 Nissan Pathfinder What's eating up my catalytic converter

1991 Nissan Pathfinder mileage: 160,000. My Nissan Pathfinder stalled a few weeks back.(It’s a 306E something engine, overhead, fuel injected.)Then we noticed a few days later that the catalytic converter was growing extremely hot. When removed it looked rotten inside. We replaced it. The new converter is not becoming red hot! There is a clunking sound in the engine. It barely runs. In the past, there was a problem with a canister under the hood that effects the fuel mixture. What's eating up my catalytic converter?