Spark plugs are a critical component of your vehicle’s ignition system. They deliver electric current from the ignition coil to the engine’s combustion chamber to ignite the air/fuel mixture. Over time, spark plugs can become worn and fail to fire properly, resulting in poor engine performance.
What are the signs that spark plugs need replacement?
There are several common symptoms that indicate your spark plugs should be changed:
- Hard starting – If your engine cranks but doesn’t start right away or requires multiple attempts before firing up, faulty spark plugs could be the reason.
- Rough idling – An uneven idle speed that surges up and down can point to issues with spark plug firing.
- Loss of power – Worn out spark plugs may cause power loss, especially under acceleration. The engine may feel sluggish.
- Reduced fuel efficiency – Poor spark timing from malfunctioning plugs reduces combustion efficiency, increasing fuel consumption.
- Misfiring – If you feel the engine misfiring or sputtering during acceleration, spark plug trouble is a possible culprit.
- Backfiring – Loud backfiring noises or popping sounds from the engine can indicate faults with spark plug firing.
- Difficulty starting when warm – Problems starting a warm engine but not a cold engine may be caused by failing plugs.
- Visible signs – Remove and inspect each spark plug. Look for excessive wear, corrosion, cracks, damage, or fouling on the plugs.
How often should spark plugs be replaced?
Most modern spark plugs will last between 30,000-100,000 miles before needing replacement. The interval can vary depending on your make/model of vehicle, type of spark plug, and driving conditions.
Here are some general spark plug replacement intervals:
- Iridium plugs – Up to 100,000 miles
- Platinum plugs – 60,000-80,000 miles
- Copper plugs – 30,000-50,000 miles
- High-performance engines – More frequent, 15,000-30,000 miles
- Frequent short trips – Change sooner
- Extensive idling – Change sooner
- Frequent stop-and-go driving – Change sooner
- Extreme driving conditions – Change sooner
Check your owner’s manual for the recommended replacement interval for your vehicle. Spark plugs should be replaced at least every 100,000 miles, even with long-life plugs.
How can I check the spark plugs myself?
It’s easy to inspect your own spark plugs between service intervals. Here’s a step-by-step guide:
- Let the engine cool completely before removing spark plugs to avoid burns.
- Clean the area around the spark plug boot before removal to prevent dirt entering the engine.
- Disconnect the spark plug boot by gently twisting it side-to-side while pulling up.
- Use a spark plug socket of the correct size and a ratchet wrench to remove the plug.
- Inspect the spark plug’s tip for wear and deposits. The tip should have light grey or brown color. Dark sooty deposits indicate a rich fuel mixture.
- Check the side electrode and center electrode for excessive corrosion and erosion. Replace if the gap exceeds specification.
- Measure the plug gap with a feeler gauge and compare to manufacturer spec. Adjust gap if needed or replace plug.
- Check for cracked insulator around center electrode that could allow voltage leakage.
- Reinstall spark plugs and connect boots, making sure you don’t cross-thread the plugs.
Look for chucks of hard debris trapped between the electrodes that could inhibit sparking. Also check that the metal band securing the ceramic insulator to the metal shell is intact.
How much does it cost to change spark plugs?
The parts cost for spark plug replacement is typically $4 – $8 per plug for standard copper plugs and up to $10 – $15 per plug for premium iridium or platinum plugs. Labor costs vary depending on the repair shop, but expect to pay $150 – $250 for spark plug replacement.
Some factories recommend changing the ignition coils when the spark plugs are replaced. This can add another $200 – $300 to the overall cost.
Here is a breakdown of typical spark plug replacement costs by vehicle type:
| Vehicle | Parts Cost | Labor Cost | Total Cost |
|---|---|---|---|
| 4-cylinder engine | $32 – $60 | $120 – $180 | $150 – $240 |
| 6-cylinder engine | $48 – $90 | $180 – $240 | $230 – $330 |
| 8-cylinder engine | $64 – $120 | $240 – $320 | $300 – $440 |
Costs may be slightly higher for difficult to reach plugs that require more labor time. To save on labor costs, you can change spark plugs yourself with some basic mechanical skills and tools.
When should I change the spark plug wires?
Spark plug wires (also called ignition wires) deliver high voltage from the distributor or ignition coil to the spark plugs. It’s recommended to replace the spark plug wires every 60,000-100,000 miles or when replacing spark plugs.
Look for the following signs that your spark plug wires need to be changed:
- Visible damage – Cracked, frayed, torn or melted wires
- Hard starting issues
- Misfiring at high speeds
- Failed emissions test
- Decreased fuel economy
- Arcing – Visible blue spark flashing on wire’s route
Replacing only the spark plugs without the wires risks continued misfires. New spark plug wires will restore maximum voltage delivery for strong spark plug firing.
How can I improve the life of my spark plugs?
You can maximize the lifespan of your spark plugs with proper maintenance:
- Follow factory tune-up schedules and replace at recommended intervals
- Use the specified spark plug for your engine
- Keep air filters clean for proper airflow
- Change engine oil regularly to avoid contaminants
- Perform regular inspections and check engine light trouble codes
- Make sure ignition timing is set correctly
- Drive conservatively avoiding sudden acceleration/deceleration
- Address any engine issues immediately to prevent damage
Spark plugs are an inexpensive maintenance item that should not be neglected. Replacing them at specified intervals will keep your engine running at peak performance. Consult your owner’s manual or mechanic for optimal spark plug service intervals.
Conclusion
Watch for common symptoms like misfires, power loss and hard starting that indicate worn spark plugs that need replacement. For most vehicles, spark plugs require changing every 30,000-100,000 miles. The cost for spark plug replacement varies by vehicle but usually ranges from $150-$400. With proper maintenance and regular replacement at the recommend intervals, spark plugs will last to their maximum lifespan. Checking and changing your spark plugs is easy preventive maintenance to keep your vehicle running smoothly.