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2003 Ford Mustang Mach 1 P0301 P0303 P0305 P0420 P0430 Diagnosis and Repair Guide

Model: 2003 Mustang Mach 1 Fault Code: P0301 Posted: 2011-06-07 10:40

Seeking help with recurring misfire and catalytic converter issues on a 2003 Ford Mustang Mach 1 4.6L DOHC V8 engine. Fault codes detected: - P0301: Cylinder 1 Misfire Detected - P0303: Cylinder 3 Misfire Detected - P0305: Cylinder 5 Misfire Detected - P0420: Catalyst Efficiency Below Threshold (Bank 1) - P0430: Catalyst Efficiency Below Threshold (Bank 2) I have already replaced the upstream oxygen sensors, spark plugs, ignition coils, and the driver's side catalytic converter. Despite these repairs, the fault codes persist. Looking for insights into potential root causes such as fuel delivery issues, ignition system faults, or downstream catalyst performance. Any advice on next steps would be greatly appreciated.

Related fault codes
P0301P0303P0305P0420
Comments (3)
Anonymous 2011-06-07 20:59

Are there any aftermarket modifications installed on the vehicle, such as exhaust systems or performance parts?

Anonymous 2011-06-07 21:12

The only aftermarket part is a single chamber exhaust system. No other modifications have been made.

Anonymous 2011-06-08 04:54

Is the exhaust modification referring to the system after the catalytic converter? What brands or models were used for the replacement parts such as spark plugs, oxygen sensors, and catalytic converters?