When replacing spark plugs what else should be replaced?
When you replace spark plugs, you should also consider replacing components that wear in the same system to prevent misfires and keep your engine running smoothly. In most cars, this means the ignition wires or coil boots, and, if your engine uses a distributor, the distributor cap and rotor. Depending on the age and maintenance history, you may also want to replace or inspect the PCV valve, the air filter, and, if accessible, the fuel filter. On modern coil-on-plug systems, faulty coils or boots are replaced as needed, and some wear items still warrant attention.
Ignition-system configurations and what to replace
Distributor-based ignition systems
Older cars and some trucks use a single distributor that routes high-voltage to each spark plug. When you service the plugs in these engines, review these related parts for wear or failure.
- Distributor cap and rotor: Replace if you see cracking, corrosion, carbon tracks, or poor rotation.
- Ignition wires (spark plug wires) or coil-on-plug boots: Replace if brittle, cracked, or very stiff, or if you’re already pulling wires for access.
- Spark plugs: Replace with the correct heat range and gap per manufacturer specs.
- PCV valve: Replace if clogged or sticky to reduce oil leaks and improve crankcase ventilation.
- Air filter: Replace to ensure clean air intake and proper fuel-air mixture.
- Fuel filter: Replace per service interval if accessible or if fuel delivery symptoms arise.
- Valve cover gasket or related gaskets: Inspect and replace if you remove the valve cover to access the plugs and detect leaks.
These items are commonly addressed when servicing spark plugs on older, distributor-equipped engines. Replacing worn components can improve starting, idle quality, and fuel efficiency.
Distributorless / coil-on-plug ignition systems
Modern engines often place the ignition coil directly over each cylinder. There are no distributor parts to wear, but the coils and boots can still fail, and related maintenance items remain relevant.
- Ignition coils or coil boots: Replace if cracked, arcing, or failing to deliver a strong spark; coil-on-plug packs are often replaced as a set if one fails.
- Spark plugs: Use the OEM-recommended type and gap; torque to spec to avoid cross-threading or overtightening.
- Electrical connectors and boots: Inspect and replace any damaged connectors or boots to maintain a good electrical connection and seal.
- PCV valve: Replace as preventive maintenance to keep ventilation clear.
- Air filter: Replace to ensure consistent engine breathing and fuel economy.
- Fuel filter: Replace according to the vehicle’s maintenance schedule, especially in older vehicles with costly fuel delivery issues.
- Valve cover gasket: If there are signs of oil seepage around the spark plug wells after removing coil packs or plugs, consider gasket replacement.
In many modern vehicles, coil and plug components dominate the ignition maintenance, but the same principle applies: replace worn coils/boots and any associated seals during a spark plug service to minimize future misfires and leaks.
Additional maintenance considerations during a spark plug service
Besides ignition components, you may also address related maintenance items to optimize performance and prevent future issues. This can include checking and topping fluids, inspecting belts and hoses, and ensuring the cooling system is in good shape. Some service intervals also call for replacing the PCV valve, air filter, or fuel filter as part of a broader tune-up.
To ensure the best results, consult your vehicle’s owner manual or service manual for the exact parts and torque specs recommended for your engine, and consider having a tech inspect for oil leaks around plug wells or damaged boots that could indicate deeper problems.
Summary
When you replace spark plugs, you should evaluate ignition components (wires or boots, coils or cap/rotor as applicable) and related wear items such as the PCV valve, air filter, and, if accessible, the fuel filter. In distributor-based systems, the cap/rotor and wires are prime targets; in modern coil-on-plug engines, coils/boots and plugs take center stage, with PCV, filters, and seals as part of ongoing maintenance. Following the manufacturer’s guidelines will help ensure reliable starts, smooth idling, and efficient fuel economy.
