Aftermarket converters are a junk car buyer's worst nightmare. Purchasing a car only to find that the converter has been replaced is a waste of time, money, and effort. Use this guide to help avoid making that costly mistake! DATE CODE: Aftermarkets often feature a date code stamped on it, something that is not found on stock OEM converters. 2. AFTERMARKET WELDING: Aftermarkets will often show signs of poor welding. Look for evidence of NON FACTORY welds as a clue it is not O