Most automobile manufacturers recommend periodically changing the spark plug wires and distributor cap. The distributor cap is responsible for distributing the electrical charge received from the ignition coil along the spark plug wires to the spark plugs. As the distributor cap and wires wear, efficiency can drop, resulting in misfires, poor running and reduced fuel economy. Fortunately, it is very easy to change the distributor cap and spark plug wires.
Some jobs under the hood require advanced tools, brawn, or specialized knowledge, but virtually anyone can change the spark plug wires and distributor cap. The only tool required is a Phillips head screwdriver. White labels or notepaper, a marking pen and Scotch tape might also come in handy. Perform this maintenance when the engine is cold to avoid burning yourself on any hot components.
If you are not familiar with what your spark plug wires and distributor cap look like, don’t worry. A local parts store only needs your vehicle’s year and model to find the parts you need. You can also order your spark plug wires and distributor cap online. If you do order online, you will have an opportunity to look at a picture of the parts before ordering. You might want to print a picture of the distributor cap and compare it against the one in your car to make sure it is the correct part.
As long as you will be replacing the spark plug wires and distributor cap, you should also replace the rotor inside the distributor. The rotor, resembling a miniature weather vane, will become visible when you remove the distributor cap. It simply pulls up/off a stem. No tools required. The new rotor presses on the same way, and the part is cheap. The rotor spins a metal arm inside the cap that can become pitted and worn.
Once you acquire the parts to replace your spark plug wires and distributor cap, take a close look at the existing spark plug wires in the vehicle. Each spark plug wire plugs into the distributor cap at a specific location on the cap. The only critical rule to follow is that this order be maintained.
The engine fires in a specific succession, which the spark plug wires and distributor cap are set up to support. Most spark plug wires and distributor caps are numbered for clarity. The #1 spark plug wire attaches to the #1 plug on the distributor cap; the #2 wire to the #2 plug, and so on. At the opposite end of the #1 spark plug wire is the #1 spark plug, or the first cylinder that fires.
The safest way to change the spark plug wires and distributor cap is to unscrew and remove the distributor cap without unplugging any spark plug wires. Note the way the cap is oriented. You might want to tape a note that says “T” at the top of the cap. There will be one extra wire that runs to the ignition coil. Unplug this wire from the cap (leaving it attached at the coil) and tag it with an “IC.” Unscrew the cap, lift it off the distributor, and set it aside by laying in on the engine.
The wedge-shaped, "weathervane" rotor will now be visible, protruding up from the distributor itself. Grip it securely and pull straight up, applying even pressure. The distributor’s rotor stem is slightly flattened on two sides. Look inside the hollow rotor stem of the new part to orient it before pushing it down on to the distributor stem.
Now install the new cap, careful to orient it the same way as the old cap. Replace all four screws and tighten securely.
Remove a single wire from the old cap and from its spark plug. If the wire is numbered, choose the corresponding number from your new kit. If the spark plug wires are not numbered, find the right wire by choosing the same length from your new kit. Plugs are various distances from the distributor cap, making them of varying lengths.
Install the new wire on to the spark plug by pushing it down securely. You should feel or hear a pop or snap. Run the new spark plug wire to the new distributor cap, following any snap-guides or rubber brackets that might be holding the wires in place along the way. Look at the old cap to be sure you plug the wire into the same location on the new cap. Repeat this procedure for each wire. Finally, install your new ignition coil wire to replace the one you tagged earlier as “IC.”
When you replace your spark plug wires and distributor cap you can also check or replace your spark plugs, if necessary. With a little basic maintenance your vehicle should run smoother and more efficiently. The cost of spark plug wires and distributor caps vary, but an average modest cost is about $50 US dollars, including the rotor.