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15% Off Online Orders of Select Parts and Accessories. Enter Promo Code MMJ15 in Cart

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15% Off All Online Orders of Select Parts and Accessories
Receive 15% Off Your Online Purchase. Use promotional code MMJ15 at checkout to receive discount. Not valid in combination with any other discounts or promotions. Not valid on gift cards, special orders, installed merchandise, commercial or fleet purchases. Excludes the following categories: Tires, Batteries, Wheels, Oil, Antifreeze, Refrigerant, Truck Boxes, Vent Visors, Bug Shields and BRANDS: 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, Champion and BBK Performance. Valid online until 2:59 am EST on 2/2/17. Online orders scheduled for in-store pick up must be completed by closing on 2/1/17 for discount to apply.

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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.

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