2003 Ford Crown Vic P71 with P0301 and P0316 Codes: Misfire, Flashing Check Engine Light at 50 mph, Power Loss
I own a 2003 Ford Crown Victoria Police Interceptor with 154,000 miles. The vehicle is showing Diagnostic Trouble Codes P0301 and P0316. I've already replaced the spark plugs and coil pack for cylinder #1. However, the check engine light flashes at speeds above 50 mph and only stops flashing when the vehicle is below that speed or in park—after which it simply illuminates. At 50 mph, the car lacks full power; it revs high but does not accelerate properly. I've also replaced several components including the intake air sensor and idle control valve. When the check engine light is flashing, the air conditioning blows warm until the light turns off or extinguishes—after which airflow returns to normal. Additionally, the battery drains significantly under these conditions. The alternator was replaced in January, along with a new RedTop battery. I've reset the vehicle's ECU both electronically and by physically disconnecting the battery. I also recently changed the transmission fluid and filter; no metal shavings were found, and the fluid condition is acceptable. I'm seeking advice on how to diagnose and resolve this persistent issue involving misfire and engine performance problems.
P0301 and P0316 indicate a cylinder misfire, which may suggest damage to the catalytic converter—especially since the flashing check engine light is a high-priority symptom. Misfires can stem from ignition, fuel delivery, or mechanical issues. You've replaced plugs and coils—did you verify spark at all cylinders, especially #1 (front passenger side)? Try using Motorcraft-style plugs for better compatibility. Check injector performance on cylinder #1 by conducting a fuel pressure test under KOEO conditions. Observe any pressure drop. Also confirm that the NOID light is pulsing normally. Next steps: perform a compression test and inspect for vacuum leaks around cylinder #1. Note: Cylinder #1 is located on the front passenger side.