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 40,000 volts 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 fuel/air mixture in the combustion chamber.
Normally, a set of spark plugs requires replacement about every 20,000-30,000 miles, on vehicles such as the Spectrum and Storm which are equipped with an High Energy Ignition (HEI) system. Any vehicle which is subjected to severe conditions will need more frequent plug replacement.
Under normal operation, the plug gap increases about 0.001 (0.0254mm) for every 1,000-2,000 miles. As the gap increases, the plugs voltage requirement also increases. It requires a greater voltage to jump the wider gap and about 2-3 times as much voltage to fire a plug at high speeds than at idle.
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 possibly lead to preignition. Pre-ignition takes place when plug tips get so hot that they glow sufficiently to ignite the fuel/air mixture before the actual spark occurs. This early ignition will usually cause a pinging during low speeds and heavy loads.
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 and 5
When removing the 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're going to get mixed up. On some models, it will be more convenient for you to remove all of the wires before you start to work on the plugs. If this is necessary, take a minute before you begin and number the wires with tape before you take them off. The time you spend here will pay off later on.
- Disconnect the negative battery cable, and if the car has been run recently, allow the engine to thoroughly cool.
- For the Storm 1.8L engine, remove the 6 Allen® head screws and the spark plug cover from the cylinder head cover.
- Using compressed air, 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.
- 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 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. If at all possible, try not to use a flexible extension on the socket. Use of a flexible extension could damage the spark plug insulator.
- Inspect the spark plugs and clean or replace, as necessary. Inspect the spark plug boot for tears or damage. If a damaged boot is found, the spark plug wire must be replaced.
- Using a feeler gauge, check and adjust the spark plug gap to 0.041 in. (1.05mm). 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.
- Carefully start the spark plugs by hand and tighten a few turns until a tool is needed to continue tightening the spark plug. Using a torque wrench, tighten the spark plug to 14 ft. lbs. (19 Nm).
- 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.
- For the Storm 1.8L engine, install the spark plug cover and tighten the 6 Allen® head screws to 124 inch lbs. (14 Nm).
- Connect the negative battery cable.