* Crankshaft Position Sensor (CKP): This sensor tells the computer the position of the crankshaft, essential for ignition timing. A faulty CKP sensor will prevent the engine from starting. This is a very common cause for this type of problem, especially in older vehicles.
* Camshaft Position Sensor (CMP): Similar to the CKP sensor, a faulty CMP sensor prevents proper timing and starting.
* Ignition System Problems: This could include issues with:
* Ignition Coil(s): One or more coils might have failed, preventing the spark plugs from firing.
* Spark Plugs/Wires: Worn, damaged, or fouled spark plugs or wires can also prevent starting.
* Ignition Control Module (ICM): This module controls the ignition system; a faulty ICM can cause starting problems.
* Fuel System Issues:
* Fuel Pump: The fuel pump might have failed or is weak, not delivering enough fuel to the engine. You might hear a weak whirring sound from the fuel pump when you turn the key to the "on" position (before cranking).
* Fuel Filter: A clogged fuel filter can restrict fuel flow.
* Fuel Injectors: Faulty fuel injectors might not be spraying fuel properly.
* Fuel Pressure Regulator: A faulty regulator might not maintain the correct fuel pressure.
* Security System: If the vehicle has a factory security system or aftermarket alarm, a fault in the system could prevent starting.
* PCM (Powertrain Control Module): While less common, a failing PCM can cause various starting and running problems.
Troubleshooting Steps:
1. Check the obvious: Ensure the battery terminals are clean and tight. A low battery can sometimes cause intermittent starting issues.
2. Listen carefully during cranking: Do you hear any unusual noises (clicking, whirring)? This can help pinpoint the problem area.
3. Check the fuel system: Listen for the fuel pump whirring when you turn the key to "on." If you don't hear it, the fuel pump might be the culprit.
4. Scan for trouble codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the PCM. This is often the fastest way to identify the problem.
5. Visual inspection: Check the ignition system components (coils, wires, plugs) for any visible damage.
Recommendation: Since diagnosing this problem requires some mechanical knowledge and tools (like an OBD-II scanner), it's best to take your Lincoln Navigator to a qualified mechanic or auto repair shop for diagnosis and repair. Attempting some of these repairs yourself without experience could lead to further damage or injury.
