Spark plug wires are a basic but very important engine component. The spark plug wire transmits the high voltage (30 thousand to 50 thousand volts) generated by the ignition coil to the spark plug. When exposed to heat and vibration, the carbon in the wires can loosen and reduce conduction between the coil and the spark plug. For optimal engine performance, spark plug wires should be replaced periodically. We'll show you how to test spark plug wires so you can check for or avoid problems like engine failure and radio static interference.
Step
Step 1. Check for symptoms
Damaged spark plug wires will show signs of deterioration which include:
- Irregular no-load state
- Engine failed to start
- Radio interference
- Reduced fuel mileage
- Failed emission test due to high hydrocarbon emissions or a faulty code indicating the cylinder does not start.
- Troubleshooting engine check light
Step 2. Check the cables
Use a flashlight or a well-lit area to do a visual inspection of the spark plug wires.
- Look for physical damage to the wires or spark plug housing such as cuts and burns.
- Check the spark plug wires and observe the insulation around the wires.
- Look for damage due to high heat from the engine compartment (burns).
- Check for corrosion between the spark plug housing, spark plug and coil.
Step 3. Start the machine
Look for an electric arc or listen for a rattling sound that indicates a high-voltage leak.
Step 4. Use jumper wires to ground the screwdriver well insulated
Pull the screwdriver in the long direction of each spark plug wire, around the coil, and the spark plug housing. If you see an arc from the wire to the screwdriver, it means that the wire is damaged.
Step 5. Use a spray bottle filled with water to spray the cable
You should spray water near the spark plug housing attached to the spark plug if you want to see arcing and fog. If an arc is found in the spark plug housing near the spark plug, turn off the engine. Then remove the spark plug housing from the spark plug and check inside the spark plug housing for any carbon footprints. If there is a carbon footprint, the spark plug will also need to be replaced.
Step 6. Perform a spark plug wire resistance test
Look for the spark plug resistance value in the vehicle manual. You can also search for it online.
Use an ohm meter to determine if the cable resistance is as recommended. Place the pins on one end of the cable, making sure they touch the metal contacts, and check that the cable resistance is within the range according to the manual
Step 7. Check the spring clips securing the cable inside the distributor cap
A damaged clip can cause the cable to slip because it does not hold the cable in position.
Step 8. Make sure your spark plugs are properly routed
Refer to the vehicle manual to assist you in this task. Cross coupling can cause energy drain.
Tips
- Do not move all the cables at once. Do it one by one then replace.
- Keep spark plugs clean to reduce conduction drain.
- Some engines have a coil-on-plug (COP) configuration that bypasses the spark plug wire completely, although the spark plug housing is still present.
- Don't assume that crossed spark plug wires are a bad sign. Some manufacturers do this to eliminate the magnetic field.
