2003 Ford Expedition 5.4L Misfire P0300 with Additional OBD II Codes - How to Diagnose and Fix
I own a 2003 Ford Expedition 5.4L 2WD with 93,000 miles. The vehicle was loaned to a church group and driven during a severe storm on highway conditions. After the drive, the OBD II scanner showed multiple misfire codes: P0300, P0306, P0316, P0351, P0352, P0353, P0354, P0355, P0356, and P0357. I understand that the coil packs are likely causing misfires, but I'm unsure which ones to replace first. I'm wondering if using a diagnostic meter with live data (such as mode 6) can help identify which specific cylinder is misfiring or if wiring damage due to moisture exposure might be the root cause. The vehicle runs but performs poorly, especially under load. There's also a noticeable absence of signals on one or two cylinders. Any advice on how to prioritize coil pack replacement or troubleshoot wiring issues would be greatly appreciated.
Mode 6 data is often the most effective way to diagnose misfiring coil packs on Ford vehicles. If your scanner supports live cylinder misfire counting, that's ideal for pinpointing faulty coils. Many users end up replacing all coil packs due to the complexity of diagnosing individual failures. Summit Racing currently offers Accelerate coil packs for Fords—some are more affordable than OEM parts. Good luck with the diagnosis and repairs; please keep us updated on your progress.