Mercury Grand Marquis catalytic converter failure causing rattling and performance issues on Mercury Grand Marquis

Some Mercury Grand Marquis owners report experiencing symptoms of catalytic converter failure, including rattling noises and decreased engine performance, which can manifest as reduced power and acceleration. These issues may arise due to a rich fuel mixture caused by problems such as a faulty upstream oxygen sensor, a malfunctioning MAF sensor, or worn spark plugs. Additionally, some owners find that driving with a bad O2 sensor contributes to catalytic converter failure, leading to increased fuel consumption and potential engine damage. The average cost for replacing a catalytic converter in a Mercury Grand Marquis ranges from $1,799 to $1,820, while repairs can cost around $600 at approximately 72,700 miles. Many owners also notice the check engine light illuminating, often accompanied by trouble codes like P0430, which indicate catalytic converter problems that should be addressed promptly to prevent further damage and maintain vehicle efficiency.