Most Likely Causes:
* Ignition System: This is often the primary suspect.
* Spark Plugs: Worn, fouled, or improperly gapped spark plugs are a very common cause of misfires, especially at low RPM where the combustion process is more sensitive. Inspect them for wear, fouling (black, oily, or white deposits), and proper gap. Replace if necessary.
* Spark Plug Wires: Cracked, worn, or loose spark plug wires can prevent a strong spark from reaching the plugs. Inspect for damage and ensure they're securely connected.
* Ignition Coil(s): The ignition coil(s) supply the high voltage to the spark plugs. A failing coil will result in weak or no spark to one or more cylinders, leading to a misfire. Testing with a multimeter or using a professional-grade ignition coil tester is needed.
* Ignition Control Module (ICM): This component controls the firing order of the spark plugs. A faulty ICM can cause misfires, often in a specific cylinder or pattern. Testing is usually required.
* Fuel System:
* Fuel Injectors: A clogged or faulty fuel injector can deliver insufficient fuel to a cylinder, causing a misfire. Cleaning or replacing injectors may be necessary. A fuel pressure test is important to rule out low fuel pressure.
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to lean conditions and misfires. Replacing the fuel filter is relatively inexpensive and easy.
* Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A faulty MAF sensor can provide incorrect readings, leading to a lean or rich fuel mixture and causing misfires. Cleaning the MAF sensor (carefully!) or replacement might solve the problem.
* Engine Management System:
* Engine Computer (PCM/ECM): While less common, a faulty engine control module can cause misfires. This is usually diagnosed through professional-level scan tools.
* Sensors: Various sensors (e.g., crankshaft position sensor, camshaft position sensor) provide the engine computer with vital information. A faulty sensor can cause incorrect fuel/air mixture calculations and misfires. These typically need testing with a scan tool.
Troubleshooting Steps:
1. Check Engine Light: If the Check Engine Light is on, use an OBD-II scanner to retrieve diagnostic trouble codes (DTCs). This can significantly narrow down the potential causes.
2. Visual Inspection: Inspect the spark plugs, wires, and ignition coil(s) for any visible damage or wear.
3. Basic Maintenance: Change the fuel filter and air filter. These are inexpensive and can resolve issues if they are clogged.
4. Testing: If the visual inspection doesn't reveal anything obvious, testing with a multimeter (for ignition components) or a professional-grade scan tool is recommended.
5. Professional Diagnosis: If you're not comfortable performing these tests, take your Ranger to a qualified mechanic for diagnosis and repair.
Important Note: Misfires can lead to further engine damage if not addressed promptly. Driving with a persistent misfire can cause catalytic converter damage, among other problems. Addressing this issue quickly is essential.
