* Spark plug issues: A fouled, damaged, or improperly gapped spark plug.
* Ignition coil problem: The ignition coil for that cylinder might be failing or faulty. Durangos of that era often have individual coils per cylinder.
* Worn or damaged spark plug wire: A cracked or corroded wire can prevent a spark from reaching the plug.
* Injector problem: A clogged or malfunctioning fuel injector is a common cause of cylinder misfires.
* Valve problems: A burnt, bent, or sticking valve can prevent proper combustion. This is a more serious issue.
* Compression issues: Low compression in the cylinder indicates problems like worn piston rings, a blown head gasket, or a damaged valve. This is also a more serious issue.
* Camshaft issues: Problems with the camshaft, lobes, or lifters could affect valve operation in that cylinder.
Troubleshooting Steps:
1. Diagnose the Problem: Before you start replacing parts, you need to identify the specific issue. The most common symptom of a problem with the fourth cylinder is a misfire. This will often be accompanied by:
* Check Engine Light (CEL): This light will illuminate and a diagnostic trouble code (DTC) will be stored in the vehicle's computer. Use an OBD-II scanner to retrieve the code. This is the *first* step.
* Rough idle: The engine will run unevenly.
* Loss of power: The engine will feel sluggish or hesitate.
* Exhaust smoke: Excessive smoke (especially blue smoke) can indicate an engine problem.
2. Check the Basics: Once you've retrieved the DTC, start with the simpler checks:
* Visual inspection: Look for obvious problems like loose or damaged wiring, cracked spark plug wires, or a visibly damaged spark plug.
* Spark plug inspection: Remove the spark plug from the fourth cylinder and inspect it for fouling, damage, or incorrect gap. Replace if necessary.
* Spark test: If you have a spark tester, test for spark at the spark plug. This helps isolate if the problem is ignition related.
3. Advanced Diagnostics (if necessary): If the simple checks don't reveal the problem, you'll need more advanced diagnostics:
* Compression test: Measures the pressure in each cylinder. Low compression points to internal engine problems.
* Fuel injector test: Checks if the injector is delivering fuel.
* Leak-down test: Helps determine if there are leaks in the cylinder's sealing surfaces (valves, piston rings).
4. Repair: Once you've identified the problem, you can perform the necessary repair. This might involve replacing a spark plug, ignition coil, fuel injector, or requiring more extensive engine work (if compression or valve issues are discovered).
Important Considerations:
* Safety: Working on a vehicle can be dangerous. Disconnect the battery's negative terminal before starting any work. Use appropriate safety equipment, including gloves and eye protection.
* Mechanical Skills: Repairing engine issues requires mechanical skills and experience. If you are not comfortable working on your own vehicle, take it to a qualified mechanic.
* Tools: You will need various tools depending on the problem, including a socket set, wrenches, an OBD-II scanner, and possibly specialized tools for compression and leak-down testing.
In short, providing a specific fix is impossible without a diagnosis. Start with retrieving the diagnostic trouble codes, then proceed with systematic troubleshooting. If you're not mechanically inclined, a professional mechanic is the safest and most efficient option.
