Fuel System:
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational position. A failing CKP sensor can cause erratic starting, sputtering, and stalling, especially under load (like during a U-turn). This is a strong suspect given the symptoms.
* Cam Position Sensor (CMP): Similar to the CKP, a faulty CMP prevents proper timing of fuel injection and ignition.
* Fuel Pump: A weak fuel pump might provide insufficient fuel pressure, leading to sputtering and stalling, especially when the engine is tilted during a U-turn. Listen carefully for the whirring sound of the fuel pump during key-on before cranking. A weak or failing pump will often make a quieter or weaker sound than normal.
* Fuel Filter: A clogged fuel filter restricts fuel flow, causing similar symptoms.
* Fuel Pressure Regulator: This regulates fuel pressure in the system. A faulty regulator can lead to inconsistent fuel delivery.
Ignition System:
* Ignition Coil: Cracked or failing ignition coils can cause misfires and sputtering. These are common in older vehicles.
* Spark Plugs and Wires: Worn spark plugs or damaged wires can cause misfires and poor combustion, resulting in sputtering and stalling.
* Distributor (if applicable): Though less common in later models, some 2000 Explorers might have distributors. Worn components within can cause ignition problems.
Other Potential Issues:
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause a lean or rich fuel mixture, leading to sputtering and stalling.
* Throttle Position Sensor (TPS): If the TPS is malfunctioning, the computer won't get accurate information about throttle position, affecting fuel and ignition timing.
* Idle Air Control Valve (IAC): This valve controls the idle speed. A dirty or faulty IAC can cause stalling at low speeds or during idle.
* Low Fuel: Sounds obvious, but make sure you actually have enough fuel.
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's operation.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any trouble codes stored in the computer. This is the most important first step.
2. Inspect Spark Plugs and Wires: Look for signs of wear, damage, or fouling.
3. Check Fuel Pressure: This usually requires a fuel pressure gauge and some mechanical skill.
4. Listen for the Fuel Pump: As mentioned above, listen for the pump's whir during key-on.
5. Inspect Vacuum Lines: Look for cracks, loose connections, or damage.
Important Note: Because the problem is exacerbated by changes in vehicle position (U-turn, driveway entry), it's strongly suspected that a sensor issue (CKP, CMP, or possibly the fuel pump's low fuel pressure under load) is the root cause. Getting a diagnostic scan from a reputable mechanic or auto parts store is the most efficient way to pinpoint the problem. Attempting repairs without proper diagnostics could lead to unnecessary expense and further damage.
