How to Test Spark Plug Wires

Article provided by wikihow the wikihow manual

A spark plug wire is an important engine component that carries the electricity produced by the ignition coil to the spark plug. The spark plug wire has 3 parts, which include a latex-coated wire and 2 boots that are placed at each end of the wire. A spark plug wire consists of a nylon or Kevlar core coated with carbon fibers followed by flexible coating and heat-resistant insulation. When exposed to heat and vibration, the carbon in the wire may loosen and reduce the conduction between the coil and the spark plug. Eventually the spark plug wires need to be replaced for optimal engine performance. If you know how to test spark plug wires, you may be able to diagnose or circumvent a variety of problems, which include engine misfires and radio static.

Steps

1. 1
   Know the possible symptoms of a defective spark plug wire. Problems with spark plug wires may include:
   • An erratic idle
   • Engine misfire
   • Radio interference
   • Decreased fuel mileage
   • A failed emissions test due to elevated hydrocarbon emissions or a fault code indicating cylinder misfire.
2. 2
   Use a flashlight or an area with good lightening 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. Determine if damage has been done due to high heat from the engine compartment.
   • Check for corrosion between the boot and the spark plug and coil.
3. 3
   Run the engine. Look for electrical arcs or listen for a snapping noise that may indicate a high-voltage electrical leak.
4. 4
   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 defective wire.
5. 5
   Perform a spark plug wire resistance test. Locate the spark plug's resistance rating in the vehicle's factory service manual. You can also search online for the resistance of after-market wires. Use an ohm meter to determine if the resistance is in compliance with the recommendations.
6. 6
   Inspect the spring clips that hold the wires in the distributor cap. Damaged clips may allow the wires to slip and not hold their proper position.
7. 7
   Determine if your spark plug wires are routed properly. Look in the vehicle's manual to help you with this task. Cross coupling can create an energy drain.

   
   

Tips

• Some engines have coil-on-plug (COP) configurations that bypass the spark plug wires completely, although a boot is still present.
• Do not assume that crossing spark plug wires is a bad sign. Some manufacturers do this to cancel out magnetic fields.
• Keep the spark plug wires clean to reduce conduction drain.

Things You'll Need

• Flashlight
• Jumper wire
• Screwdriver with insulated handle
• Ohm meter

Article provided by wikihow the wikihow manual. Please edit this article and find author credits at the original wikiHow article on How to Test Spark Plug Wires. All content on wikiHow can be shared under a Creative Commons license.