* Injector Problem: A clogged or faulty injector in cylinder 3 is a very common cause. Fuel injectors deliver fuel to the combustion chamber. If the injector is clogged, it won't deliver enough fuel, leading to a misfire. A faulty injector might be intermittently working or completely dead. Testing the injector's spray pattern and electrical signal is crucial.
* Ignition Coil (or Pack): While you replaced the wires, the ignition coil (or coil pack, depending on the engine) could be the issue. A failing coil can't deliver enough voltage to the spark plug in cylinder 3, resulting in a misfire. A visual inspection for cracks or damage is a good start, but testing with a multimeter is necessary to confirm its functionality.
* Worn or Damaged Valve: A bent, burned, or otherwise damaged valve in cylinder 3 will prevent proper combustion. This requires a more involved inspection, possibly needing a compression test to confirm.
* Compression Issues: Low compression in cylinder 3 suggests a problem with the piston rings, cylinder walls, or head gasket. A compression test is essential here to diagnose this.
* Camshaft Position Sensor (CMP Sensor) or Crankshaft Position Sensor (CKP Sensor): These sensors tell the computer the engine's rotational position. A faulty sensor can cause the computer to mistime the spark or fuel injection, leading to a misfire.
* EGR Valve Issues: The Exhaust Gas Recirculation (EGR) valve can cause misfires if it's sticking open or closed improperly, affecting the air/fuel mixture.
* Mass Airflow Sensor (MAF) Sensor: If the MAF sensor is faulty and providing inaccurate readings, the engine computer will deliver an incorrect fuel/air mixture which may also cause misfires.
* Vacuum Leak: A vacuum leak in the intake system can affect the air/fuel mixture, leading to misfires.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect the wiring harness connected to cylinder 3's components for any damage.
2. Compression Test: Perform a compression test to check the compression in all cylinders. Low compression in cylinder 3 points to internal engine problems.
3. Fuel Injector Test: Test the injector in cylinder 3 for proper spray pattern and electrical signal.
4. Ignition Coil/Pack Test: Test the ignition coil (or coil pack) for proper voltage output.
5. Sensor Checks: Check the CMP sensor, CKP sensor, MAF sensor and EGR valve. Sometimes a simple cleaning of these components can solve the problem.
6. Vacuum Leak Check: Carefully inspect all vacuum hoses and connections for cracks or leaks.
Important Note: Diagnosing this issue correctly requires some automotive knowledge and tools. If you're not comfortable performing these tests, it's best to take your Explorer to a qualified mechanic for diagnosis and repair. Attempting complex repairs without the necessary skills could lead to further damage.
