Replacing spark plug wires is necessary when your vehicle runs poorly in damp weather or rain, or when called for in the vehicle maintenance schedule. Done properly, and with quality parts, the replacement of spark plug wires results in a better running engine and better gas mileage.

Spark Plug Firing Order

Spark plug wires must make the proper connection from the distributor cap or coil pack to the spark plugs; spark plug, or ignition, wires are not randomly connected. To make the proper connection, a guarantee it is always best to replace one wire at a time, connecting each to the distributor and spark plug before the next if replaced. If all the wires are removed prior to replacement, it becomes necessary to determine the firing order of the engine, the direction of distributor rotation and which cylinder is the number one cylinder. Engines do not fire the cylinders one after the other. A four-cylinder engine will not have a firing order of 1-2-3-4, but typically will use a firing order such as that of a Honda Accord: 1-3-4-2. As not all engines use this firing order, you must determine the firing order for your vehicle by consulting a repair manual, asking your dealer or doing a web search. After determining the firing order, remove the distributor cap and have someone crank the engine for you. Observe the rotation of the ignition rotor---this is the distributor rotation direction. Rotate the engine until the number one cylinder is at top dead center (TDC). Check the timing marks on the front crankshaft pulley (generally) to determine this. Note where the distributor rotor is pointing in relation to the towers on the cap, the tower the rotor is aligned with is where you will insert the wire for the number one spark plug. Install the cap back on the distributor and install the wire to the number one cylinder. Then, following the rotation of the distributor install the remaining wires according to the firing order. If you have done this properly, and if the engine has no other problems, it should run smoothly when started.