The cause could be several things, including:
* Spark plug issues: A fouled, worn, damaged, or improperly gapped spark plug in cylinder 5.
* Ignition coil problem: The ignition coil for cylinder 5 could be failing or faulty.
* Worn or damaged spark plug wire: If your Ranger still uses individual spark plug wires (less common on newer vehicles), the wire for cylinder 5 might be damaged.
* Injector problem: A clogged or faulty fuel injector in cylinder 5 could prevent proper fuel delivery.
* Low compression: Low compression in cylinder 5 indicates a problem with the valves, piston rings, or head gasket. This is a more serious issue.
* Vacuum leak: A vacuum leak can affect the air/fuel mixture and cause a misfire.
Troubleshooting Steps (in general order of easiest to most difficult):
1. Check the spark plug in cylinder 5: Inspect it for fouling, wear, damage, or incorrect gap. Replace if necessary.
2. Inspect the ignition coil for cylinder 5: Look for obvious damage. A simple swap test with another coil (if possible) can quickly determine if the coil is at fault.
3. Check the spark plug wire (if applicable): Inspect for cracks, fraying, or damage. Replace if necessary.
4. Check the fuel injector for cylinder 5: This is more involved and might require specialized tools or professional diagnosis.
5. Perform a compression test: This will determine if there's a mechanical issue within the cylinder. Low compression in cylinder 5 indicates a serious problem.
6. Check for vacuum leaks: Inspect all vacuum hoses and connections for cracks or leaks.
Important Note: Before you start troubleshooting, make sure there are no other related codes. Sometimes, another problem (like a bad crankshaft sensor) can trigger multiple misfire codes. A proper OBD-II scan tool can provide more detailed information than just the P0305 code. If you're not comfortable working on your vehicle, it's best to take it to a qualified mechanic for diagnosis and repair.
