How to Change Spark Plugs
Replacing worn spark plugs can greatly improve your engine’s performance and efficiency, and it can be done at home with basic hand tools. Recommended spark plug replacement intervals can range from 30,000 miles to every 100,000 miles, and they vary widely by car manufacturer and spark plug metal types and design. You will need to follow the recommendations in your owners’ manual. It’s OK to upgrade but never down grade from the manufactures factory requirements. Doing so will hinder performance and may cause issues related to sister components or the engine itself.
Spark plugs fire constantly and wear down over driving time, reducing their efficiency. Spark plug replacements can be challenging on some vehicles engines. The greatest challenges you’ll face is accessibility and sticking components such as when removing the spark plug wires or ignition coils/boots and unscrewing the spark plugs. Some spark plugs can be difficult to reach and require removal of the upper plenum/intake manifold. In these cases, a new plenum gasket will be needed. Check the Repair Guide for your specific vehicle and engine.
How to Change Spark Plugs
1. Safety First
Park your vehicle on a flat, dry surface and ensure the engine is cool. Clean the engine area of any dirt and debris to prevent anything from falling into the engine cylinder during spark plug replacement. Additionally, you may want to disconnect the battery (negative post only). Check the vehicle repair guide or other resources to ensure no damage will occur if the battery is disconnected for any length of time or if any modules or other items would need to be reprogrammed. Ensure the positive and negative terminals do not become crossed with a foreign object such a hand ratchet and cause a dangerous short circuit.
2. Remove the Spark Plug Wire
First, remove any interference items. If your vehicle requires removal of the upper intake plenum, a new gasket will be needed. After gaining access, you will likely find the rubber spark plug wire end and inside metal terminal somewhat difficult to remove from the spark plug. You must be careful to avoid damaging the rubber boot or tearing the wire terminal away from the plug wire end. If you discover the plug wire boot is ‘stuck’ to the spark plug try using spark plug wire pliers to aid in removal. The boot may need to be twisted back and forth to break the bond from the spark plug. Again, be careful. The metal terminal that connects to the spark plug inside the boot must be removed simultaneously with the boot to avoid damage. If damage to the boot or wire occurs, don’t feel bad. In many instances, even a professional is unable to remove them without damage occurring. If damage does occur, the wire(s) must be replaced. Re-installing a damaged boot or wire will cause a misfire and possible damage to other ignition components. If the spark plug wires are five to seven years old or have 100K+ miles of use, replacement is highly recommended. A new plug wireset will ensure the newly installed spark plugs will receive all the necessary firepower from the ignition coil(s).
3. Remove the Coil On Plug (COP)
COP designed coils attach directly to the spark plug end and use a long rubber insulator boot. Start the removal process by disconnecting the electrical connector from the ignition coil. Press down or pull up on the locking tab to make the connector release so it can be disconnected. A small screwdriver may be needed to help depress the locking tab. Once the connector is off, remove the hold down bolt and carefully twist the coil about a quarter turn or so back and forth until the ‘bond’ is broken. Then it should pull straight up and out. Use caution! There is always a risk of damage to the COP boot. COP coils and their insulator boots are made of plastic and rubber that protect and insulate the high voltage conducting materials inside. Damage will cause the high voltage to leak (short) to ground causing a misfire and possible damage to other ignition components. If the boots are damaged they must be replaced. Just like spark plug wires, if they are five to seven years old or have 100K+ miles of use, replacement is highly recommended. Check the COP boots for signs of engine oil or engine anti-freeze contamination. Oil puddled in the spark plug well hole is usually caused by a valve cover tube seal and/or leaking O-ring. The appearance of coolant in the plug well can be caused by a leaking heater or by-pass hose or even the intake manifold gasket. These leaks should be repaired first, especially if severe, to prevent damage to the new components.
4. Unscrew the Spark Plug
Be sure the engine is cooled off. Use a spark plug socket to remove the spark plugs. Avoid thread damage by following these suggested steps. On COP applications remove debris by blowing air down into the spark plug well hole. Even the tiniest of particles can build up in the threads of the spark plug during removal and cause damage to the cylinder head threads. If this occurs, sometimes a spark plug thread restorer tool may be used to do just that, restore damaged threads in the cylinder head. Next, loosen/turn the spark plug about a half a turn counter-clockwise and blast a small shot of penetrant fluid to the base/ thread area of the spark plug. Allow a few minutes to soak. On some engines, the manufacture may provide additional removal steps. Check the repair guide. Take note it you feel considerable resistance while turning the spark plug counter-clockwise. You may need an additional small amount of penetrant and soaking time. If you encounter resistance, turn the spark plug clockwise and carefully work it back and forth. If the plug just won’t co-operate, you should probably stop and seek a professional’s help. Damaged cylinder head threads can often be expensive to repair, depending on your vehicle.
5. Put in the New Spark Plugs
Before installing the new spark plugs, ensure each plug part number matches the part number and box description. Inspect each new spark plug for damage. Ensure the threads are clean and straight, the electrode and tip are intact, and the insulator for the plug wire or COP boot is not cracked or chipped. Some brands of spark plugs come ‘pre-gapped’ and require no ‘re-gapping’. For these spark plugs, make sure the tip is not bent or damaged. For other brands and plug types, check the gap to make sure it matches your engines plug gap specification. A gapping gauge tool is available from AutoZone. A small amount of anti-seize maybe used on most but not all spark plug brands and types. Check the box or the plug manufacture. Install each new spark plug, being careful not to cross-thread and damage the spark plug and cylinder head threads. Be sure and tighten to the proper amount of torque. Check your owner’s manual or the spark plug box. You will need a torque wrench, available at your local AutoZone.
6. Re-install the Spark Plug Wires or Ignition Coils (COP)
Apply a small amount of plug wire grease to the plug wire boot (or COP boot) and re-install each plug wire or ignition coil. Be sure and connect the plug wires to the appropriate spark plug for each engine cylinder (refer to a firing order diagram if necessary). Re-install the coil hold down bolt(s). Re-attach the electrical connector(s). Re-install all other components removed to gain access. Be sure and gather up all tools and the engine is free and clear to start. Remember to re-connect the battery if it was disconnected at the beginning.
7. Start Up the Engine
Starting the engine after the spark plug replacement is a good way to validate your work. Note: If your Check Engine Light is on, you can drive your vehicle to your local AutoZone store and have the code translated. If the Check Engine Light ‘flashes’ there is a cylinder miss-fire. Re-check your work. Do not drive the vehicle very far if the engine is missing as the catalytic converter could be damaged.
You may need to gap your spark plugs before installing them. Some plugs come pre-gapped, and if this is the case it will say so on the box. Otherwise you’ll need a gap tool to gap your new plugs according to the specifications in your owner’s manual. Most modern cars use plugs made from long-lasting materials, so you might only need to do a spark plug replacement once or twice over the time you own a vehicle.