Most Common Causes:
* Spark Plugs and Wires: Worn, fouled, or damaged spark plugs are a very common cause of misfires. Similarly, cracked or loose spark plug wires can prevent a proper spark from reaching the plug. These are relatively inexpensive and easy to check and replace.
* Ignition Coil(s): The ignition coil(s) provide the high voltage needed to create the spark. A failing coil can cause a misfire in one or more cylinders. Testing a coil requires a multimeter or specialized tool.
* Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A faulty MAF sensor can cause a lean or rich fuel mixture, leading to misfires. Cleaning it might solve the problem, but replacement may be necessary.
* Crankshaft Position Sensor (CKP): This sensor tells the engine's computer where the crankshaft is in its rotation. A faulty CKP sensor can prevent the engine from firing correctly, causing a misfire.
* Camshaft Position Sensor (CMP): Similar to the CKP sensor, a faulty CMP sensor can disrupt the timing of the engine and cause misfires.
* Fuel Injectors: A clogged or faulty fuel injector can prevent sufficient fuel from reaching a cylinder, resulting in a misfire. Testing fuel injectors typically requires specialized tools.
* Vacuum Leaks: Leaks in the intake manifold or vacuum lines can disrupt the air/fuel mixture, leading to misfires.
Less Common, but Still Possible Causes:
* Damaged or worn valve(s): A bent or damaged valve can prevent proper combustion.
* Low fuel pressure: A problem with the fuel pump or fuel filter can reduce fuel pressure, leading to a misfire.
* Faulty PCM (Powertrain Control Module): While less likely, a failing PCM can cause various engine problems, including misfires. This is generally the most expensive and difficult to diagnose/repair.
Troubleshooting Steps:
1. Check engine codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored by the engine control module. This can provide valuable clues about the source of the problem.
2. Inspect visually: Look for obvious signs of damage to spark plugs, wires, vacuum lines, etc.
3. Start with the easiest and cheapest: Begin by checking and replacing the spark plugs and wires, as these are the most frequent culprits.
4. Seek professional help: If you're not comfortable performing these checks yourself, take your Expedition to a qualified mechanic for diagnosis and repair.
Remember safety first! Disconnect the negative battery terminal before working on any electrical components in your engine bay. If you're unsure about anything, it's always best to consult a professional.
