I’ve got a 2004 Ford Expedition 5.4 with 437k miles. I keep getting a misfire in cylinder one. I’ve replaced the injector, plugs, and coil packs. Used a Noid light to test, and everything checks out. Runs fine under light acceleration, but when I’m pulling my trailer or going uphill and need more throttle, it misfires in cylinder one.
Oil level stays steady, and compression is good on every cylinder:
I couldn’t get my compression tester into cylinders 4 and 8 (if you know, you know—big pain back there).
Compression’s actually close to factory (around 120) for a motor with this many miles. I’m out of ideas and would love some input on what to check next. Hitting 500k miles has become a bit of a hobby since I’ve got other vehicles, but I still drive this one almost every day.
Thanks in advance! I’m just a shade tree mechanic turned infantry grunt who grew up doing my own repairs, and I still refuse to pay anyone to turn a wrench unless it’s an alignment or tires.
Did you see any wetness on the plug boots or corrosion on the plugs or boots when you pulled them out? Have you changed the springs and boots on the coil packs?
@Jade
I’ve seen rockers come completely off and cause only a slight miss at idle. Burnt valves can sometimes show as a lean code and only slightly lower compression. Best to do a leak-down test. A borescope with an articulating end can also help spot burnt valves. Since you’ve covered the basics and have good signals from the injector and coil pigtails, I’d start looking for a mechanical issue.