* Spark Plug and Wire: The spark plug in cylinder #1 is the most common cause. It could be fouled, cracked, worn out, or loose. The spark plug wire could be damaged, loose, or cracked, preventing a good spark. Check this first. It's the cheapest and easiest fix.
* Ignition Coil: If the spark plug and wire are okay, the ignition coil (or a specific coil pack if it has individual coil packs per cylinder) for cylinder #1 could be failing. This is less common than a bad spark plug but still relatively easy to test or replace.
* Injector: A clogged or faulty injector for cylinder #1 would prevent fuel from reaching the combustion chamber. Testing this requires a bit more expertise and specialized tools.
* Compression: Low compression in cylinder #1 means the engine isn't building sufficient pressure to ignite the air/fuel mixture properly. This could be due to worn piston rings, a damaged valve, or a blown head gasket. Checking compression requires a compression tester. This is a more serious and potentially expensive problem.
* Wiring/Connector Problems: A broken or corroded wire in the ignition system or a faulty connector could interrupt the spark or fuel signal to cylinder #1.
* PCV Valve: A problematic Positive Crankcase Ventilation (PCV) valve can lead to excessive crankcase pressure, affecting combustion and causing misfires.
Troubleshooting Steps:
1. Visual Inspection: Start with a visual inspection of the spark plug wire and spark plug in cylinder #1. Look for any obvious damage, loose connections, or corrosion.
2. Spark Plug Test: Remove the spark plug and inspect it. If it's fouled (covered in oil, fuel, or carbon), replace it. If possible, test the spark with a spark tester to ensure it's producing a strong spark.
3. Swap Components (If Possible): If you suspect the spark plug wire or coil, try swapping it with a corresponding part from another cylinder (if it's a coil-on-plug system, you can only swap the coil). If the misfire moves to the other cylinder, you've found the faulty part.
4. Professional Diagnosis: If you can't find the problem after these steps, take your Expedition to a qualified mechanic. They have the tools and expertise to diagnose more complex issues like injector problems, compression problems, or wiring faults.
Remember to always disconnect the negative battery terminal before working on any electrical components in your vehicle. Safety first!
