* Federal Emissions Standards: Catalytic converters are regulated to meet specific emission standards for your vehicle's year and engine. Using a converter not designed for your specific vehicle model and year could result in your vehicle failing emissions testing. This could lead to fines. The part numbers you listed (Magnaflow 46005 and 45004) are likely for different applications, and only one might be legal for your vehicle.
* Internal Design and Efficiency: Different converters have different internal designs that affect their efficiency in reducing pollutants. A converter designed for a different vehicle might not be as effective at reducing emissions from your 3.4L V6 Alero engine, potentially leading to a failed emissions test.
* Oxygen Sensor Placement: The location and type of oxygen sensors are critical. The converter needs to have the correct number and type of sensor bungs (threaded holes) in the correct locations to interface properly with your vehicle's oxygen sensors. Incorrect placement can lead to incorrect readings and engine malfunction.
* Backpressure: The catalytic converter affects exhaust backpressure. An improperly matched converter can significantly alter backpressure, potentially damaging your engine or causing performance issues.
In short: While both converters *might* physically fit your exhaust, only one might meet legal emissions requirements. You must verify that the chosen converter is specifically designed and approved for a 2002 Oldsmobile Alero with a 3.4L V6 engine. Check the Magnaflow website or a reputable parts supplier's website using your vehicle's Year, Make, Model, and Engine to ensure compatibility and legality. Using the part number alone is not sufficient. Using an incorrect converter carries significant risks, and you should only use a part confirmed as suitable.
