See Figure 1
A typical spark plug consists of a metal shell surrounding a ceramic insulator. A metal electrode extends downward through the center of the insulator and protrudes a small distance. Located at the end of the plug and attached to the side of the outer metal shell is the side electrode. The side electrode bends in at a 90° angle, so that its tip is just past and parallel to the tip of the center electrode. The distance between these two electrodes (measured in thousandths of an inch or hundredths of a millimeter) is called the spark plug gap.
The spark plug does not produce a spark, but instead provides a gap across which the current can arc. The coil produces anywhere from 20,000 to 50,000 volts (depending on the type and application) which travels through the wires to the spark plugs. The current passes along the center electrode and jumps the gap to the side electrode, and in doing so, ignites the air/fuel mixture in the combustion chamber.
Spark plug life and efficiency depend upon the condition of the engine and the temperatures to which the plug is exposed. Combustion chamber temperatures are affected by many factors such as compression ratio of the engine, air/fuel mixtures, exhaust emission equipment and the type of driving you do. Spark plugs are designed and classified by number according to the heat range at which they will operate most efficiently.
SPARK PLUG HEAT RANGE
See Figure 2
Spark plug heat range is the ability of the plug to dissipate heat. The longer the insulator (or the farther it extends into the engine), the hotter the plug will operate; the shorter the insulator (the closer the electrode is to the block's cooling passages) the cooler it will operate. A plug that absorbs little heat and remains too cool will quickly accumulate deposits of oil and carbon since it is not hot enough to burn them off. This leads to plug fouling and consequently to misfiring. A plug that absorbs too much heat will have no deposits but, due to the excessive heat, the electrodes will burn away quickly and might possibly lead to preignition or other ignition problems. Preignition takes place when plug tips get so hot that they glow sufficiently to ignite the air/fuel mixture before the actual spark occurs. This early ignition will usually cause a pinging during low speeds and heavy loads. In severe cases, the heat may become high enough to start the fuel/air mixture burning throughout the combustion chamber, rather than just to the front of the plug, as in normal operation. At this time, the piston is rising in the cylinder while making its compression stroke. The burning mass is compressed and an explosion results, forcing the piston back down in the cylinder while it is still trying to go up. Obviously, something must "give'' and, in this type of situation, pistons are often damaged.
The general rule of thumb for choosing the correct heat range when picking a spark plug is: if most of your driving is long distance, high speed travel, use a colder plug; if most of your driving is stop and go, use a hotter plug. Original equipment plugs are generally a good compromise between the 2 styles, and most people never have the need to change their plugs from the factory recommended heat range.
REMOVAL & INSTALLATION
See Figures 3, 4, 5, 6, 7 and 8
A set of conventional spark plugs usually requires replacement after about 20,000-30,000 miles (32,000-48,000 km), depending on your style of driving. In normal operation, plug gap increases about 0.001 in. (0.025mm) for every 2,500 miles (4,000 km). As the gap increases, the plug's voltage requirement also increases. It requires a greater voltage to jump the wider gap and about two to three times as much voltage to fire the plug at high speeds than at idle. The improved air/fuel ratio control of modern fuel injection, combined with the higher voltage output of modern ignition systems, will often allow an engine to run significantly longer on a set of standard spark plugs, but keep in mind that efficiency will drop as the gap widens (along with fuel economy and power).
Since they tend to resist wear better than conventional plugs, platinum-tipped spark plugs have longer maintenance intervals. Under normal operating conditions, they only need replacing every 60,000 miles (96,500 km) or 48 months, whichever comes first. Always refer to the spark plug manufacturer's recommendations.
When removing spark plugs, work on one at a time. Don't start by removing the plug wires all at once, because, unless you number them, they may become mixed up. Take a minute before you begin and number the wires with tape.
- Disconnect the negative battery cable. If the vehicle has been run recently, allow the engine to thoroughly cool.
On CA16DE and CA18DE Pulsar engines, the ornament cover (and its 8 screws) must be removed to gain access to the spark plugs. These engines have a Direct Ignition System, which does not use spark plug wires; instead, individual ignition coils are fitted directly to each spark plug.
- Carefully twist the spark plug wire boot to loosen it, then pull upward and remove the boot from the plug. Be sure to pull on the boot and not on the wire, otherwise the connector located inside the boot may become separated.
- Using compressed air, if available, blow any water or debris from the spark plug well to assure that no harmful contaminants are allowed to enter the combustion chamber when the spark plug is removed. If compressed air is not available, use a rag or a brush to clean the area.
Remove the spark plugs when the engine is cold, if possible, to prevent damage to the threads. If removal of the plugs is difficult, apply a few drops of penetrating oil or silicone spray to the area around the base of the plug, and allow it a few minutes to work.
- Using a spark plug socket that is equipped with a rubber insert to properly hold the plug, turn the spark plug counterclockwise to loosen and remove the spark plug from the bore.
The cylinder head is aluminum, which is easily stripped. Remove the plugs ONLY when the engine is cold. If removal is difficult, loosen the plug only slightly and drip penetrating oil onto the threads. Allow the oil time enough to work and then unscrew the plug. If removal is still difficult, retighten and loosen until the plug comes free. Proceeding in this manner will prevent damaging the cylinder head threads. Be sure to keep the socket straight to avoid breaking the ceramic insulator. During installation, coat the plug threads with oil or anti-seize compound to ease future removal.
- Inspect the spark plug boot for tears or damage. If a damaged boot is found, the spark plug wire must be replaced or repaired.
New spark plugs come pre-gapped, but double check the setting. The recommended spark plug gap is listed in the Tune-Up Specifications chart. Do not check or adjust the gap, however, on platinum-tipped plugs, since platinum is brittle and the electrode would break.
- Using a wire feeler gauge, check and adjust the spark plug gap. When using a gauge, the proper size should pass between the electrodes with a slight drag. The next larger size should not be able to pass while the next smaller size should pass freely.
- Using the electrode bending tool on the end of the gauge, bend the side electrode to adjust the gap, if necessary. Never attempt to adjust the center electrode.
- Lightly lubricate the threads of the replacement plug and carefully thread it into the bore by hand. If resistance is felt before the plug is almost completely threaded, back the plug out and begin threading again. In small, hard to reach areas, an old spark plug wire and boot could be used as a threading tool. The boot will hold the plug while you twist the end of the wire, and the wire is supple enough to twist before it would allow the plug to crossthread.
- Carefully tighten the spark plug. If the plug you are installing is equipped with a crush washer, seat the plug, then tighten about 1 / 4 turn to crush the washer. If you are installing a tapered seat plug, tighten the plug to 14-22 ft. lbs. (19-30 Nm).
It is a good practice to use a torque wrench to tighten the spark plugs on any vehicle, especially the aluminum head type.
- Apply a small amount of silicone dielectric compound to the end of the spark plug lead or inside the spark plug boot to prevent sticking, then install the boot to the spark plug and push until it clicks into place. The click may be felt or heard, then gently pull back on the boot to assure proper contact.
INSPECTION & GAPPING
See Figures 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20