High-Probability Issues:
* Crankshaft Position Sensor (CKP Sensor): This sensor tells the computer the engine's rotational speed and position. A faulty CKP sensor will prevent the engine from running or cause it to stall unexpectedly. This is a very common cause of this problem in older vehicles.
* Cam Position Sensor (CMP Sensor): Similar to the CKP sensor, but this one monitors the camshaft. A malfunctioning CMP sensor can also lead to the engine cutting out without warning.
* Mass Airflow Sensor (MAF Sensor): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause erratic engine behavior, including stalling.
* Ignition System Problems: This includes:
* Ignition Coil(s): A failing coil can cause a cylinder to misfire, leading to stalling, especially under load.
* Spark Plugs and Wires: Worn or damaged spark plugs or wires can prevent proper ignition, causing the engine to die.
* Distributor Cap and Rotor (if applicable): Older vehicles may have a distributor; worn components can interrupt the spark.
* Fuel System Issues:
* Fuel Pump: A failing fuel pump might not deliver sufficient fuel pressure, causing the engine to stall. Listen for the fuel pump whirring when you turn the key to the "on" position – if you don't hear it, it could be the culprit.
* Fuel Filter: A clogged fuel filter can restrict fuel flow and cause stalling.
* Battery and Alternator: A weak battery or failing alternator might not provide enough power to keep the engine running, especially if other components are drawing a lot of current.
Less-Likely (But Still Possible) Issues:
* Computer (PCM) Problems: A faulty PCM (Powertrain Control Module) can cause a wide range of issues, including random stalling. This is a more complex and expensive diagnosis.
* Wiring Harness Problems: Damaged or corroded wiring can interrupt signals to various components, leading to intermittent engine failure.
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's operation, causing stalling.
Troubleshooting Steps:
1. Check the Obvious: Start with the easy checks: Check the battery terminals for corrosion, ensure the fuel level is adequate, and listen for the fuel pump priming sound when the ignition is turned on.
2. Check Engine Light: If the check engine light is on, get the diagnostic trouble codes (DTCs) read using an OBD-II scanner. This will give you a starting point for diagnosis. Auto parts stores often offer free code reading.
3. Visual Inspection: Inspect the wiring harness for any obvious damage or corrosion.
4. Professional Diagnosis: If you're not comfortable working on your vehicle, take it to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately.
Important Note: Safety first! If your Expedition is stalling unexpectedly, avoid driving it until the problem is diagnosed and fixed. Continuing to drive with an intermittent problem could lead to a dangerous situation.
