The catalytic converter was stopped up after replacing it the van runs good unless you give all gas at once how can this be fixed?

If the van runs well except when you press the accelerator all the way down, it's possible that the new catalytic converter is not functioning properly. Here are a few things to check:

1. Check the catalytic converter for proper installation. Make sure the catalytic converter is properly connected to the exhaust system and that there are no leaks.

2. Check the oxygen sensors. The oxygen sensors are located upstream and downstream of the catalytic converter. They monitor the amount of oxygen in the exhaust and help the engine control unit (ECU) adjust the air/fuel mixture. If the oxygen sensors are not working properly, the ECU may not be able to adjust the air/fuel mixture correctly, which can cause the engine to run rich and damage the catalytic converter.

3. Check the fuel injectors. The fuel injectors spray fuel into the engine's cylinders. If the fuel injectors are not working properly, they may not be delivering the correct amount of fuel, which can cause the engine to run rich and damage the catalytic converter.

If you have checked all of these things and the van is still running poorly, you may need to have the catalytic converter replaced again.