Unit 1Spark plug wire checking
Spark plug wire description
According to Wikipedia, high tension leads or high tension cables or spark plug wires or spark plug cables are the wires that connect a distributor, ignition coil, or magneto to each of the spark plugs in some types of internal combustion engine. "High tension lead" or "cable" is also used for any electrical cable carrying a hight voltage in any context. When exposed to heat and vibration, the carbon in the wire may loosen and reduce the conduction between the coil and the spark plug. For optimal engine performance, spark plug wires should be replaced periodically. In this unit we will teach you how to test spark plug wires so that you may be able to diagnose or circumvent a variety of problems, including engine misfires and radio static.
TO KNOW MOREIf you want to know how High Voltage is produced in the ignition coil, click the next link:
/ Ignition coil
1.1How to test spark plug wires
- Visual inspection
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. 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.
- 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 a multimeter to determine if the resistance of the wire is in compliance with the recommendations:
Put the Function/Range Switch in 20 Kohm position.
Mark the wires with the number of the cylinder.
Unplug the spark plug wires carefully.
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.
Writethe results in the attached form.
Plug the spark plug wires to each spark plug of the cylinders respecting the ignition order (eg. 1-3-4-2)
Start up the engine and check its right performance
HIGHLIGHTSAll measurements made on the spark plug wires of the same engine, must be equal or very similar. If some wire has a very different resistance value respect to the other ones, it must be replaced.
1.2Results
Fill in the form the results and measurements of the tests:
Spark plug wire 1 / Spark plug wire 2 / Spark plug wire 3 / Spark plug wire 4Visual inspection
Resistance test (in KΩ)
All images are from This site is covered by the Creative Commons license.
1
TMV01-Ignition system / Unit 1