1. Distributor Cap and Rotor: While you mentioned that the distributor cap and rotor have not been replaced, they can still cause misfires if they are worn out or damaged. Check for cracks, corrosion, or carbon tracking on the distributor cap. The rotor should also be inspected for any damage or wear.
2. Ignition Coil: The ignition coil supplies the spark plugs with the necessary voltage to create a spark. A weak or failing ignition coil can cause misfires. Check the coil for any visible damage or cracks, and test its resistance with an ohmmeter to ensure it meets the manufacturer's specifications.
3. Vacuum Leaks: Vacuum leaks can lean out the air-fuel mixture, causing misfires. Inspect all vacuum hoses for cracks or disconnections. You can also use a smoke machine to identify any hard-to-find vacuum leaks.
4. Fuel Pressure: Low fuel pressure can also lead to misfires. Check the fuel pressure using a fuel pressure gauge to ensure it meets the manufacturer's specifications.
5. EGR System: A faulty EGR (Exhaust Gas Recirculation) system can affect the air-fuel mixture and cause misfires. Check the EGR valve and its associated hoses and solenoids to make sure they are functioning properly.
By addressing these potential causes, you can narrow down the issue and hopefully resolve the engine misfires.
