What You Need to Change and Gap Your Plugs

Airman fixing a battery.

If you've decided that you can get at your spark plugs without damaging your vehicle, assemble the items you need before you begin:

  • An old blanket, mattress pad, or padded car protector to place over the fender where you'll be working to protect it from scratches: Commercial car protectors often come with handy pockets that hold tools and little parts while you work. You can make such a pocket yourself by pinning up the bottom edge of your folded blanket or pad.
  • Work clothes: Wear something that you don't mind getting stained with grease, oil, and other stuff. Changing spark plugs may be simple, but it can get messy. Trust me.
  • Hand cleaner.
  • Clean, lint-free rags: You'll use these to wipe the spark plugs clean, wipe the cleaner off your hands, and generally tidy up after the work is done.
  • A work light (or flashlight, at least).
  • A new set of spark plugs: Buy one for each cylinder in your engine. And don't be shocked if you're told that you need eight spark plugs for your 4-cylinder engine. Some engines require two spark plugs per cylinder.

    Never change just a few plugs; it's all or nothing for even engine performance. If you're feeling especially wealthy, buy an extra plug in case you get home and find that one of them is defective, or in case you accidentally ruin one by dropping and cracking it or by cross-threading it when you install it. If you don't use it, keep it in your trunk compartment tool kit for emergencies. Spark plugs don't get stale.

  • Anti-seize compound and silicone lubricant (optional): The threads of the spark plugs should be lightly coated with a dab of engine oil off the oil dipstick or with anti-seize lubricant before you install them in theengine. Also, if there are rubber boots on your spark plug wires, apply silicone lubricant to them to prevent them from sticking to the porcelainpart of the spark plug. (Silicone boots don't need this.)
  • A wire or taper feeler gauge: You use this to gap spark plugs.
  • A small set of basic socket wrenches that includes a ratchet handle and a spark plug socket.

Buying the Right Plugs

To buy the proper spark plugs for your vehicle, you must know its specifications (or "specs," as they're often called). Your owner's manual may have specifications for buying and gapping the spark plugs on your vehicle. If you don't have an owner's manual, or if yours lacks the necessary information, you can find the correct spark plugs and spark plug gap in a general "Tune-Up Specification Guide" (called a "spec sheet," for short) at an auto supply store. These guides are either in pamphlet form or printed on large sheets, like the one in Figure 6-1, that are displayed near the parts section of the store. If you can't find a spec sheet at the store, ask a salesperson to show it to you. For a sample spec sheet, see Figure 6-1. I've italicized the examples in the list ofbasic information below so you can find them on the figure.

To obtain the specs for your particular vehicle, you need some basic information. All this information should be in your owner's manual, and most of it is also printed on metal tags or decals located inside your hood. You can usually find these in front of the radiator, inside the fenders, inside the hood — anywhere the auto manufacturer thinks you'll find them. I know of one vehicle that has its decal inside the lid of the glove compartment. These identification tags also provide a lot of other information about where the vehicle was made, what kind of paint it has, and so on, but don't worry about that information right now. Here's what you need to know to obtain the specs for your vehicle:

  • The make of the vehicle (Toyota, Chevrolet, and so on).
  • The model (Prius, Malibu, and so on).
  • The model year (2004, 1999, and so on).
  • The number of cylinders and type of engine.
  • Whether the vehicle has an automatic or a manual (standard) transmission.
  • The engine displacement: How much room there is in each cylinder when the piston is at its lowest point? (For example, a 3-liter 6-cylinder engine has a displacement of one-half liter, or 500 cubic centimeters — usually shown as 500 CCs — in each cylinder.) The bigger the displacement, the more fuel and air the cylinders in the engine hold.

    The displacement of engines on older vehicles may be listed in cubic inches, such as 302, 350, 454, and so on. Modern vehicles are usually listed in liters (1.8, 2.3, 5.9) or cubic centimeters (2200, 3400, 3800).

  • The kind of fuel system: If your engine is fuel-injected, you may need to know whether your car has throttle body injection or multi-port injection. Carburetors, on the other hand, were distinguished by how many "barrels" they had.
  • Whether the vehicle has air conditioning: It's not usually necessary to take this into account when buying most parts, but you never knowwhen you'll need it.
Figure 6-1: Ignition specifications for a 2004 Toyota Prius.

Tip: If you haven't already done so, enter your vehicle's make, model, year, and number of cylinders on a copy of the Specifications Record in Appendix B. If your owner's manual has the model number of the plug you need and the size of the gap, enter that information, too. If not, take the record with you to thestore and use their spec sheet to fill in the necessary information.

Caution: At the auto supply store, don't just ask a salesperson which type of plug you should buy — you have a very good chance of getting the wrong one. First look up the specifications yourself, and then ask for the plug by number. Ifyou're unsure, have a salesperson double-check it for you.

Look up your vehicle by make and model under the proper year on the spec sheet at the store. (For example, for my first car, Tweety Bird, a "previously owned" 1967 Mustang, I looked under 1967, then under Ford, then under Mustang, then under "200 cu. in. 6 Cyl. Eng. (1 bbl.)" — which means that Tweety had an engine displacement of 200 cubic inches, a 6-cylinder engine, and a single-barrel carburetor.) Then write down the following information from the spec sheet in the appropriate columns on your Specifications Record:

  • The spark plug gap: This is the amount of space that there should be between the center and side electrodes of each spark plug.
  • The part number for the spark plugs designed for your vehicle.

From Auto Repair for Dummies, copyright © 2009 by Wiley Publishing, Inc., Indianapolis, Indiana. Used by arrangement with John Wiley & Sons, Inc.

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