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01 mustang v6 misfires

I had a problem a couple of years ago with a misfire cylinder 6. After new plugs, wires, mass airflow sensor, throttle body,and fuel filter I still had the miss. As a last resort In replaced the coil pak. Problem solved. Same problem again last week but no codes replaced the coil pak took the car out for test drive, ran great. Next day the car ran worse than before and had a coil failure code. Now sometimes the car runs OK sometimes not hot cold doesn’t matter. Any ideas before I spring for a new coil pak?

There’s one thing you might want to check. The coil pak has it’s own fuse. But between that fuse and the coil pak is the radio interference capacitor. If this thing has failed, the coil pak might not be seeing full voltage. The capacitor is located at the top front of the engine.

Tester