1. Ignition System: This is the most likely culprit. The problem is likely affecting cylinders in a pattern suggesting a problem in the ignition system's distribution.
* Distributor Cap and Rotor: Cracks, corrosion, or worn contacts in the distributor cap and rotor can cause misfires on specific cylinders. Inspect for any visible damage. A simple test involves checking for arcing while the engine is running (use caution!).
* Ignition Wires: Worn, cracked, or improperly routed spark plug wires can lead to misfires. Inspect for damage, especially near the distributor cap and spark plugs. A simple visual inspection will suffice.
* Distributor: Worn or malfunctioning points (if equipped) or a bad electronic ignition module can affect the timing and spark delivery to half the engine. A mechanic's inspection or testing is often needed for diagnosis.
* Coil: A weak or failing ignition coil won't provide sufficient voltage to all plugs. Testing the coil's output is necessary.
* Spark Plugs: Worn, fouled, or damaged spark plugs can misfire. Replace all spark plugs as they age regardless.
2. Fuel Delivery System: While less likely to affect only every other cylinder, it's still possible.
* Fuel Pump: A weak or failing fuel pump might not provide sufficient pressure to all cylinders, though this would likely cause more widespread problems.
* Fuel Filter: A clogged fuel filter restricts fuel flow.
* Carburetor: A faulty carburetor, specifically a problem with its metering system or jets, could lead to an uneven fuel distribution, although this is less likely to specifically affect every-other cylinder. If it's a carbureted engine, pay close attention to this.
3. Compression Issues: Though less probable for this specific symptom, low compression in every other cylinder could be a factor (though that would usually affect the crank and the overall power). This is worth checking only after confirming there are no ignition or fuel issues.
Troubleshooting Steps:
1. Visual Inspection: Start with a thorough visual inspection of all ignition components, fuel lines and filters.
2. Spark Test: Use a spark tester to check for spark at each spark plug. This will immediately pinpoint whether the problem is ignition-related.
3. Compression Test: If the spark test is good, perform a compression test to check for mechanical issues in the cylinders.
4. Fuel Pressure Test: Check fuel pressure to ensure the fuel pump and system are delivering sufficient fuel.
Important Note: Diagnosing engine problems can be complex. If you're not experienced with automotive repair, it's best to consult a qualified mechanic. Working on a vehicle's ignition system requires caution to avoid electrical shock.
