A simple DIY (Do-It-Yourself) tune up is something that for the most part is easy to slip your mind as it’s something most people don’t notice they need until an ignition component has failed and the car develops a misfire.

If your vehicle has platinum/iridium spark plugs, most manufacturers suggest replacing the spark plugs around 100,000 miles. If your vehicle has copper resistor spark plugs, the suggested replacement interval is typically around 30,000 miles.

After thousands of miles (and millions of combustion cycles), the tips of the spark plugs can become contaminated with the byproducts of today’s fuels, or by issues caused by leaking piston rings/engine gaskets (coolant or oil inside the combustion chamber). This can lead to driveability concerns.

The gap of the spark plug can also be significantly widened. This means that the spark has to travel further and lowers your car’s fuel economy and can lead to driveability concerns as well.

Now, the real purpose of this post is to show you what can happen if you replace ONLY your spark plugs when you do your tune up.

The truck was a 2000 Ford Ranger 4×4 with a 3.0L V6. The customer had requested that we replace his spark plugs as preventive maintenance but not the spark plug wires. He chose Denso spark plugs, which I personally would not have. Autolite and Motorcraft are the suggested Ford plugs.

See those black marks on the white porcelain? That’s called carbon tracking. The plug wire is actually arcing through the side of the spark plug rather than just the top part that it clips on to.

The plug wire is breaking down and creating a low resistance path for electrons to flow. Once that path is established, it’s impossible to get rid of completely, which is why replacing both the plug and the wire/boot is the only fix. Since the wire is the root of the problem, it needs to be corrected. However, if you ONLY do that, the path on the side of the spark plug is already established and this is where the spark is going to travel. Path of least resistance.

Due to this problem, the truck had a misfire (as it should), and this was because of an improper spark pattern.

It’s always a good idea to do spark plug wires at the same time as your spark plugs to ensure that you don’t have a driveability concern afterward.