2003 Ford Expedition Misfire and Lean Mixture Code

Don't worry about the lean code yet. Diagnose the misfire first. Fixing that will likely take care of the lean condition.

The most likely cause of the misfire is water snuck in past the ignition coil for cylinder 2. Once any arcing started, it will leave a carbon track behind, and that carbon will continue to short out the spark voltage. You may need to replace the spark plug and the coil. First remove that coil and check for water. Erase the fault code, then switch the the coil for cylinder 2 with one of the other ones. If a new misfire code sets for the cylinder you moved coil 2 to, replace that coil.

When you have a misfire due to missing spark, you'll have unburned fuel and air going into the exhaust system. That's where the excessive unburned oxygen will be detected as a lean condition. At the same time, you'll smell the unburned fuel at the tail pipe. Noses don't detect oxygen and oxygen sensors in the exhaust don't detect fuel.