See Details

35% Off Online Orders of Select Hard Parts. Enter Promo Code MMJ35 in Cart.

Close (X)

Receive Up To 35% Off Your Online Purchase Of Select Parts And Accessories
Use promotional code MMJ35 at checkout to receive 35% off the following categories: Select Brake Parts, Select Hi-Performance and Truck Accessories, Batteries, Paint, Splash Guards, Select Ventvisors & Bug Shields, Springs & Spacers, Water Pumps, Belts, A/C Parts, Starters, Alternators, Fuel Pumps, Radiators, Radiator Fans, Thermostats, Caps & Clamps, Clutches, Spark Plugs, Plug Wires, CV Axles, Battery Chargers & Booster Cables, OE Locks, Rack & Pinons, Window Motors, RainX Wipers, Appearance Chemicals, Floor Mats, Lift Equipment, Hand Tools, Travel Accessories, Car Covers, Seat Covers, Wheel Covers, Body Repair, Collectibles and Apparel.

Use promotional code MMJ20 at checkout to receive 20% off the following categories: Ignition, Shocks & Struts, Chassis, Jumpstarts, Air Filters, Oil Filters, Bearings & Seals, Engine Parts, Wash Accessories, Outdoor Lifestyle, Towing, Mini Air Compressors, Tire Repair Accessories, Mufflers, Grease/Oil, Additive Chemicals, P/S Pumps, Cooling Product, Timing Belts, Specialty Tools, Radiator Hose, Motor Mounts, Mirrors, Lug Nuts, Sealants/Adhesives, Fuel Filters, P/S Hoses, Gas Cans, Oil Change Accessories, Help, Wiper Motors, Loaner Tools, Air Compressors, Horns, Books, Distributors, Sun Control and Exhaust Adapters.

Use promotional code MMJ15 at checkout to receive 15% off the following categories: Test Equipment, Power Tools, Emergency Supplies, Electronics and Stereo & Accessories (MAP pricing Exclusions).

Offers not valid in combination with any other discounts, promotions or items already on sale. Not valid on gift cards, special orders, installed merchandise, commercial or fleet purchases. Those products that are included in these offers will be displayed in product search results and product detail pages. Excludes the following brands: WeatherTech, Champion, Powerstop, Razor, Traxxas, Superchips, Hypertech, Edge, Bully Dog, Diablo, Edelbrock, Holley, NOS, Proform, Specialty Auto, Autometer, Accel, K&N, Kenwood, Pioneer, Sony, Thule, Thule Karrite, JVC, Flowmaster, Hurst, B&M, MSD, Moog, Wagner, Philips, Fanmats, K-Source and BBK Performance. Valid online until 11:59 PM EST on 11/26/17.

Receive 10% Off Wagner branded brake parts with your online purchase. Use promotional code: WAGNER10.

Receive 20% Off Select Champion branded products with your online purchase. Use promotional code: CHAMP20.

Receive 10% Off Select FelPro branded products with your online purchase. Use promotional code: FELPRO10.

Free Shipping on Orders Over $50 or in-store pickup

Spark Plugs



Spark Plugs

Most vehicles on the road today are equipped with spark plugs. Changing your vehicle's spark plugs at the appropriate mileage intervals is an important part of keeping your vehicle operating efficiently. Most spark plugs are relatively inexpensive and can be properly installed by novice to intermediate level DIY'ers.

What is a Spark Plug and how does it work

What is it?

  • A spark plug is a device used in a gas fueled internal combustion engine. It is threaded into the cylinder head and its tip protrudes into the combustion chamber.
  • Its purpose is to create a spark to ignite the air/fuel mixture that keeps the engine running.

How Does it Work?

  • A spark plug channels the energy from your vehicle?s ignition coil across an air gap in the combustion chamber.
  • This spark ignites the compressed fuel/air mixture within each cylinder and the resulting combustion initiates the engines power stroke.

How is it Made?

  • A spark plug is made up of a center electrode, ground electrode, resistor (in most cases) and a terminal stud that are assembled inside a ceramic insulator.
  • This insulator assembly is then inserted into a steel shell that is designed to thread into the cylinder head.

Why Does it Fail?

  • Electrode Erosion.
  • Fouling.
  • Resistor Burnout.
  • Material Failure.

What are the Symptoms of Failure?

  • Check Engine Light.
  • Misfire.
  • Hesitation.
  • Hard Starting.

What are the Implications of Failure?

  • Poor Fuel Economy.
  • Poor Engine Performance.
  • Dead Cylinder(s).
  • Engine Damage.

How Difficult is the Install?

Difficulty Rating:


  • Installation difficulty depends on vehicle and engine size/position.

Related Parts

Return to Parts Guides