Depending on the technology your car has based on its model year, you may have the old distributor with cap and rotor and sparkplugs, your ignition coils are controlled by the computer, or you have the coil-on-plug technology where each spark plug has its ignition coil that’s controlled by the computer. The coil-on-plug ignition coils are found on newer cars from the 2000s.
1) What is the Engine Firing Order?
When you learn the firing order you learn which plugs are which. This is important in diagnosing which plug or cylinder was named in the engine code; P0300, P0301, P302, etc.
2) Ignition Coil On Faulty Cylinder
Now that we have identified the faulty cylinder remove the mounting bolt from the ignition coil, make sure the electrical connector is disconnected, and remove the ignition coil from the misfiring cylinder.
3) Inspect the Ignition Coil Visually
Look closely over the ignition coil. You are looking for signs of wear and degradation. This may include cracks or crumbling in the plastic, black and white deposits at the boot or signs of scorching.
4) Inspect the Spark Plug
Remove the spark plug and look at it closely. You are looking for signs of black soot, white deposits, or other signs of damage, wear or scorching.
5) Now Let’s Test the Ignition System
a) If you happen to have an advanced scan tool, you can run and test the engine with that. It will monitor the system and report if other issues exist.
b) If you don’t have one of those advanced scan tools you can test the ignition system by swapping the suspected bad plug and coil with another. Start by removing the ignition coil and spark plug from a cylinder that tested bad and swapping it with one from another cylinder that tested good. Now clear the codes on your engine and start it up. Plug in your OBDII and see if the codes moved with the suspected bad cylinder.
If the misfire code moved with the suspected bad plug and coil, then they were the issues. Replace the plug and coil with new ones and you are all set.