Spark Plug Troubleshooting Methods

There are two methods to troubleshooting spark plug wires. The first is the backyard mechanic technique, which is simple and only requires basic hand tools, while the other is a more sophisticated method that requires a multimeter.

Quick Troubleshooting

If you don't have a multimeter, follow this method. Begin by removing the spark plug cover on the valve cover. Then pull the spark plug wire off the spark plug with a spark plug puller or needle nose pliers. Be sure to pull from the base of the wire, because they tend to seize onto the spark plug. If you don't pull from the base of the wire, you risk breaking the wire and getting it stuck on the plug, which then becomes very difficult to remove. Next, connect an extension and spark plug socket to your ratchet, and remove the spark plug. Then place the spark plug back in the wire and place it next to a good engine ground. An engine ground is any metallic object connected to the chassis of your vehicle. Next, have a helper crank the vehicle while you observe the spark arcing from the spark plug to the engine ground. If the spark is dark blue, then you know the wires are good. If the spark is faint and yellow, you could have a faulty spark plug wire. However, this technique isn't very accurate for pinpointing the problem that might be affecting your vehicle. A more consistent and accurate method is to use a multimeter.

Multimeter Troubleshooting

If you don't have a multimeter, it is highly advisable to purchase one as it comes in handy for electrical troubleshooting. To check if the wire is faulty, set the multimeter to the "Ohms" setting and connect the black lead to one side of the spark plug wire and the red lead to the other side of the wire. You should see about 5,000 Ohms of resistance per foot of wire. This is a general rule of thumb, and will vary from vehicle to vehicle. But what is important and what you really need to look for is for an Ohm reading out of the ordinary. If the multimeter reads "Infinite" or "Ouch," then it is telling you that there is a break in the wire and that it should be replaced. If the multimeter reads an excessive Ohm reading, more than the specifications for your car, the wire should also be replaced in this scenario.