his how-to shows you how to replace your spark plugs. Your plugs should typically be replaced every 30,000 miles, and checked at 15,000 miles. I think I let mine go a little too long ;) You can tell a lot about the state of your engine by examining your spark plugs. For this how-to, I installed AC Delco Rapidfire spark plugs. AC Delco is the best brand of spark plug for our engines. There is generally no gain from performance spark plugs, so you don't need to waste your money. AC Delco is the proven-best plug for GM engines. Depending on the condition of your current plugs, you may notice a smoother running engine and a gas mileage improvement, but don't expect a miracle ;)

As long as you are doing this, you might want to replace your wires at the same time.

Gather up all your parts and tools. Most plugs come pre-gapped, but it is a good idea to check them with a gapping tool anyway. They should be gapped to .045 inches

We will start with the front three plugs, since they are the easiest and will help you get familiar with the procedure before you tackle the back three. Remove the spark plug wire from each plug by pulling and twisting on the boot. Lay the wires out of the way, but don't mix them up. If you are worried about mixing up the wires, just remove one at a time.

Once you have the wires off, it is time to remove the plugs. Be sure you are doing this on a cold engine, as removing the plugs when the engine is hot can cause severe damage to the threads in the aluminum heads! Slide the spark plug socket (this is a special socket with a rubber boot inside that protects and holds the spark plug inside the socket for easy installation and removal) onto the plug you are removing. For cylinders 4 & 6 (middle and righthand side), use a 2.5" extension on the end of the socket, and 4.5" extension on cylinder 2 (cylinder on the left).

When the plug is completely unscrewed, it will stay stuck in the socket so you can easily pull it out of the head

To install the new plugs, first you may wish to put some antiseize compound on the threads, to make them easier to remove and prevent head damage in the future. Then stick the plug into the end of the socket and insert it into the cylinder. Remove and install one plug at a time, replacing each plug right away to be sure no debris falls into the cylinder. Start threading the plug by hand, using the socket extension to turn with. Be sure you do not cross-thread the plugs, as it will cause severed damage to the threads in the heads! Screw the plug in as tight as you can by hand before cinching it down with the ratchet. If the plug doesn't feel like it is going in right, unscrew it and start again. Tighten the plug down snug.

Once you get the front three plugs replaced, reinstall the plug wires. You should feel them snap in place. Be sure to route them correctly. See the diagram below if you get the routing mixed up.

Now is time to move on to the dreaded back three. These really aren't as bad as some people make them to be. It just takes a tad longer than the front. To gain easier access to these plugs, remove the strut tower brace, if your car is so equipped. The 4 bolts should be 13mm.

Remove the spark plug wires just as you did on the front.

Remove the plugs by using the 2.5" extension for cylinders 1 & 3 (left and middle) and the 4.5"extension for cylinder 5 (right cylinder). Some people prefer to use a swivel socket, but using these extensions will all you the proper clearance. It is just a matter of wiggling your arm down behind the engine. This is a time where being a super-chunk is going to be a disadvantage.

Reinstall the plugs using the same procedure as you did for the front. Then reinstall the wires.

Once all the plugs and wires are reconnected, fire up the car. Make sure it is running alright. If it is running rough, sounds like crap and the engine is shaking violently, you either have some plug wires mixed up, or you don't have a plug wire fully seated on the plug, causing that cylinder not to fire. Double check all connections. One you are sure all is good, reinstall the strut tower brace.

Now is a good time to examine your plugs. The appearance can tell you a lot about what is going on inside your engine. A couple of my plugs were pretty heavily coated in ash. See the chart below to analyze your plugs. If you keep the plugs lines up as you remove them, you will know the condition of each specific cylinder. Hopefully you don't discover anything too serious.

Go take your car for a spin! You probably won't notice any performance gains unless your old plugs were really bad, but it is routine-maintenance money well spent.