Symptoms of a Bad CMP Sensor:
* No Start: This is the most common and obvious symptom. The engine cranks but won't fire.
* Rough Running/Misfires: The engine may run roughly, stumble, hesitate, or misfire, especially at idle or under load.
* Check Engine Light (CEL): The CEL will illuminate, and a diagnostic trouble code (DTC) related to the camshaft position sensor will be stored (likely a P0340, P0341, P0342, or P0345, depending on the specific failure). You'll need an OBD-II scanner to read the codes.
* Stalling: The engine may stall unexpectedly.
* Poor Fuel Economy: A malfunctioning CMP sensor can lead to inefficient fuel combustion.
How to Investigate a Suspected Bad CMP Sensor:
1. Check the Diagnostic Trouble Codes (DTCs): This is the *first* step. Use an OBD-II scanner to read the codes. A code related to the CMP sensor strongly suggests it's the culprit.
2. Visual Inspection: Inspect the CMP sensor itself. Look for:
* Obvious damage: Physical damage to the sensor, wiring, or connector.
* Loose connections: Make sure the connector is securely plugged into the sensor. Corrosion can also be a problem.
* Oil leaks: Oil leaking onto the sensor can cause malfunctions.
3. Check the Wiring: Inspect the wiring harness leading to the CMP sensor for breaks, chafing, or corrosion. A multimeter can be used to test continuity and resistance if you have some electrical knowledge.
4. Resistance Test (Advanced): This requires a multimeter and the knowledge of the correct resistance values for your specific CMP sensor (consult a repair manual). If the resistance is outside the specified range, the sensor may be faulty. *Caution:* Incorrectly performing this test could damage your vehicle's electronics.
5. Sensor Replacement (Final Step): If you've ruled out other issues (like a bad crankshaft position sensor, fuel delivery problems, or ignition issues), replacing the CMP sensor is the next step. It's relatively inexpensive and easy to replace, usually requiring only basic tools.
Important Considerations:
* Other Sensors: A faulty crankshaft position sensor (CKP sensor) can cause similar symptoms. It's crucial to test or rule out other potential causes before replacing the CMP sensor.
* Repair Manual: A repair manual specific to your 1999 Ford 4.0L engine will provide detailed information on sensor location, testing procedures, and replacement instructions.
* Professional Help: If you're not comfortable performing these checks or replacing the sensor yourself, take your vehicle to a qualified mechanic.
By systematically checking these points, you can increase your chances of correctly identifying whether the camshaft position sensor is at fault. Remember that properly diagnosing car problems often requires a methodical approach and the use of diagnostic tools.
