Possible Causes:
* Ignition System: This is the most likely culprit.
* Worn spark plugs: These are the easiest to check and replace. Look for excessive wear, fouling (black, oily, or white deposits), or damage.
* Worn spark plug wires: Inspect for cracks, fraying, or damage. A simple visual inspection isn't always enough; a spark tester can confirm if each wire is delivering a strong spark.
* Distributor cap and rotor: Cracks or corrosion in the distributor cap or worn rotor can interrupt the spark delivery. Inspect for these issues.
* Ignition coil: A failing coil can't supply enough voltage to the spark plugs. Testing with a multimeter is recommended. Often, a coil will exhibit intermittent failure, making diagnosis tricky.
* Ignition control module (ICM): This module controls the ignition system. A faulty ICM can cause misfires. Diagnosis typically requires a scan tool or specialized testing equipment.
* Fuel System:
* Fuel injectors: Clogged or failing fuel injectors can deliver insufficient fuel to one or more cylinders, causing misfires. Testing fuel injector pressure and flow is necessary.
* Fuel pump: A weak or failing fuel pump might not deliver enough fuel pressure. Measure fuel pressure to check.
* Fuel filter: A clogged fuel filter can restrict fuel flow. This is a relatively inexpensive and easy component to replace.
* Engine Management System:
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor can cause incorrect fuel/air mixture, leading to misfires. Cleaning the sensor (carefully!) or replacing it may resolve the issue.
* Throttle Position Sensor (TPS): A malfunctioning TPS can affect the engine's fuel delivery, contributing to misfires.
* Computer (ECM): While less common, a faulty engine control module can cause various problems, including misfires. This is usually the last thing to suspect and requires specialized diagnostic tools.
* Other Potential Causes:
* Vacuum leaks: Leaks in the vacuum system can disrupt the engine's operation and cause misfires.
* Camshaft or Crankshaft Position Sensors: These sensors provide crucial timing information to the engine computer. Faulty sensors can disrupt ignition timing and lead to misfires.
* Worn valve seals or other internal engine problems: Though less likely to cause an intermittent misfire, significant wear can cause this. This would usually be accompanied by other symptoms like oil consumption or low compression.
Troubleshooting Steps:
1. Listen to the engine: A misfire often makes a noticeable ticking or sputtering sound. Try to pinpoint which cylinder(s) is/are misfiring.
2. Visual inspection: Carefully inspect spark plugs, wires, distributor cap, and rotor for visible damage.
3. Basic checks: Check fuel pressure, inspect fuel filter.
4. Use a code reader: A code reader (OBD-I for this year) can provide diagnostic trouble codes (DTCs) that pinpoint potential problems. While not as sophisticated as later OBD-II systems, it will provide clues.
5. Spark test: Use a spark tester to check for strong sparks at each spark plug wire.
6. Compression test: A compression test can help determine if there are internal engine problems affecting one or more cylinders.
Important Notes:
* Safety First: Disconnect the negative battery terminal before working on any electrical components.
* Systematic Approach: Follow a logical order when troubleshooting, starting with the easiest and most likely causes.
* Professional Help: If you're not comfortable performing these checks, take your Ranger to a qualified mechanic. Misfires can lead to further engine damage if left unaddressed.
This detailed information should help you diagnose the misfire. Remember to be methodical and patient; pinpointing the exact cause might require some trial and error.
