Spark Plug Maintenance

How does a spark plug work?
To ignite the air/fuel mixture. Electrical energy is transmitted through the spark plug jumping the gap in the plugs firing end if the voltage supplied to the plug is high enough. This electrical spark ignites the fuel/air mixture in the combustion chamber.

A vehicle that is running rough or misfiring can cause catalytic converter damage. Preventative maintenance is the key, have your spark plugs inspected and replaced when the gap is beyond what is specified by the vehicle manufacturer.

  • Check for symptoms: Defective spark plug wires leave tell-tale signs of their deterioration, including:
    An erratic idle
    Engine misfire
    Radio interference
    Decreased fuel mileage
    Check engine light

  • Inspect the wires: Use a flashlight or an area with good lighting to perform a visual inspection of the spark plug wires.
    Look for physical damage to the wires or boots such as cuts and scorch marks
    Check the spark plug wire and examine the insulation around the wire
    Look for damage due to high heat from the engine compartment (scorch marks)
    Check for corrosion between the boot and the spark plug and coil

  • Run the engine: Look for electrical arcs or listen for a snapping noise that may indicate a high-voltage electrical leak

  • Use a jumper wire to ground a well-insulated screwdriver: Drag the screwdriver down the length of each spark plug wire, around the coil, and the boots. If you see an arc from a wire to the screwdriver, you have a defective wire. Remember to wear rubber gloves.

  • Use a spray bottle with water to spray down the wires: Spray near the boots that attach to the spark plugs to see if any arcing occurs, and if mist is present. If arcing is found at the boot near the spark plug, turn off the engine. Then remove the boot from the plug and check inside the boot for carbon tracking. If carbon tracking is present, the spark plug will also need to be replaced.

  • Perform a spark plug wire resistance test: Locate the spark plug’s resistance rating in the vehicle’s factory service manual. Use an ohm meter to determine if the resistance of the wire is in compliance with the recommendations. Place the probes on either end of the wire lead making sure they touch the metal contacts, and verify that they’re within the range called for in the manual.

  • How to use a spark plug tester: Spark plug misfire, or spark miss is when the sparks jumping the gap of the electrodes are inconsistent in their timing. This can cause your engine to stumble, lose power and even emit black smoke (due to unburned fuel not being ignited in the combustion chamber). The following steps can be taken to check if you are experiencing spark plug misfire.
    Disconnect the spark plug lead from the spark plug.
    Connect your spark plug tester to the spark plug lead.
    Connect the spark plug tester to the spark plug creating a link from the lead to the spark plug.
    Start the engine and watch the gap in the spark plug tester to see if there is inconsistent timing.

  • Determine if your spark plug wires are routed properly: Look in the vehicle’s manual to help you with this. Cross coupling can create an energy drain.

  • Cleaning a spark plug: Disconnect the spark plug lead. Clean the area around the spark plug to avoid getting debris in the combustion chamber when you remove the plug. Remove the spark plug by using a spark plug socket wrench. Using a wire brush and spray on plug cleaner, remove light deposits from the plug. If there are still difficult deposits DO NOT use a shot blaster or abrasives to clean your spark plug.

For optimal engine performance spark plugs should be replaced periodically. See an authorized dealer if you are unsure of any procedure, to have your spark plugs checked and/or changed or if you have additional questions.