* Messing up the car's computer: The car's computer (Engine Control Unit or ECU) monitors various sensor inputs, including those from oxygen sensors located before and after the catalytic converter. These sensors measure the oxygen content in the exhaust. Without a catalytic converter, the post-cat oxygen sensor will detect unusual readings, leading to a check engine light and potentially triggering the computer to enter a "limp mode" to protect the engine. This limp mode can significantly reduce engine performance and fuel economy. The ECU might try to compensate for the missing converter, but it may not be able to do so effectively, leading to misfires or other issues.
* Ruining gas mileage: While a catalytic converter doesn't directly impact fuel *efficiency* in the way, say, a faulty air filter would, removing it indirectly leads to worse gas mileage. The reasons are:
* Engine Inefficiency: The ECU's attempts to compensate for the missing converter can result in less efficient combustion, leading to higher fuel consumption.
* Increased Emissions: Without the converter cleaning up harmful exhaust gases, the engine may run less efficiently, again contributing to poorer gas mileage.
In short, removing a catalytic converter is a bad idea for both performance and legality. It's a crucial emission control device, and tampering with it can lead to significant problems and hefty fines in many places.
