* Emissions Controls: The catalytic converter is a crucial part of your vehicle's emission control system. Removing it will cause it to fail emissions testing (if required in your area) and potentially lead to fines.
* Oxygen Sensor Readings: The oxygen sensors in your exhaust system monitor the amount of oxygen in the exhaust gases. These readings are used by the ECU to adjust the air/fuel mixture for optimal performance and emissions. Removing the catalytic converter drastically alters the exhaust flow and composition, leading to inaccurate readings from the oxygen sensors. This will cause the ECU to try and compensate, potentially leading to a rough idle, poor fuel economy, hesitation, and even misfires. The ECU itself won't be "messed up", but its ability to correctly control the engine will be severely hampered.
* Backpressure: The catalytic converter offers a degree of backpressure in the exhaust system. Removing it can alter the exhaust flow significantly. While some modifications might benefit from reduced backpressure, simply removing the cat without other modifications almost always leads to negative consequences in this case.
* Check Engine Light: You'll almost certainly trigger a check engine light, indicating a malfunction in the emission control system.
In short, removing the catalytic converter is not recommended. It won't directly damage the ECU (the "chip"), but it will significantly disrupt the engine's operation and potentially damage other components over time due to improper air/fuel mixtures and excessive heat. If you're looking for performance gains, consider other modifications that won't compromise your vehicle's emissions or proper functioning.
