My KIA 2004 Sorento jeep was emiting a whistling sound on throtling and had very low power. The check engine light is on. It was discovered that the converters at the exhaust maifold are hollowed and the exhaust system was blocked. Another bigger catalyst converter distal to the ones at the manifold was blocked. This blocked or plugged converter was replaced with a good one and the vehicle is now okay but with the check engine indicator still on. But my question is, what will now be the general performance of my vehicle as I was not able to replace the catalyst in the converter at the manifold? Will it affect my gas mileage so much or ...? (Remember the converter at the manifold is now hollow and the sensor wires intact)