What Are Some Ways to Diagnose an Engine Misfire?

The best way to diagnose an engine misfire is by testing each of the components that most commonly cause misfires: spark plugs, plug wires, the coils and the fuel-delivery system. More serious issues could involve the pistons, rods and crank bearings.

Begin by removing the spark plugs and checking for signs of improper fuel burning, such as carbon build-up. If the spark plugs are not the issue, observe the wires in a dark room while the car is running. Sparks jumping from the wires may indicate that the wires are cracked and need to be replaced. Lastly, check the ohm ratings of your primary and secondary coils, ensuring that they are within manufacturer’s specifications.

While you can use a code reader to extract any error codes from the ECU that might indicate component failures, these codes are not specific enough to point you to the faulty component.