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 even with, and parallel to, the tip of the center electrode. The distance between these two electrodes, measured in thousandths of an inch or millimeters, is called the spark plug gap. The spark plug in no way produces a spark but merely provides a gap across which the current can arc. The coil produces voltage which travels to the spark plugs via wires. The current passes along the center electrode and jumps the gap to the side electrode, and, in do doing, ignites the air/fuel mixture in the combustion chamber. Resistor spark plugs are used in all engines and have resistance values of 6,000-20,000 ohms when checked with at least a 1000 volt tester.
Remove the spark plugs and examine them for burned electrodes and fouled, cracked or broken porcelain insulators. Keep the plugs arranged in the order in which they were removed from the engine. An isolated plug displaying an abnormal condition indicates that a problem exists in the corresponding cylinder. Replace the spark plugs with new ones every 30,000 miles (48,000 km).
Undamaged low mileage spark plugs can be cleaned and reused. After cleaning, file the center electrode flat with a small point file or a jewelers file. Adjust the gap between the electrodes to the following value of 0.048-0.053 in. (1.2-1.3mm) on the 3.3L and 0.033-0.038 in. (0.8-0.9mm) on the 3.5L engine.
Always tighten spark plugs to the specified torque. Over-tightening can cause distortion and change spark plug gap. Tighten the spark plugs to 20 ft. lbs. (28 Nm).
On spark plugs with normal wear, the few deposits present will be probably light tan or slightly gray in color with most grades of commercial gasoline. There will not be evidence of electrode burning. Gap growth will not average more than approximately 0.001 in. (0.025mm) per 1000 miles (1600 km) of operation. Spark plugs that have normal wear can usually be cleaned, have the electrodes filed and regapped, and then reinstalled.
Some fuel refiners in several areas of the United States of America have introduced a manganese additive (MMT) for unleaded fuel. During combustion, fuel with MMT coats the entire tip of the spark plug with a rust color deposit. The rust color deposits could be misdiagnosed as being caused by coolant in the combustion chamber. MMT deposits do not affect spark plug performance.
SPARK PLUG HEAT RANGE
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 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 in some instances, preignition may result. Preignition 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 compromise plugs, but most people never have occasion to change their plugs from the factory-recommended heat range.
REMOVAL & INSTALLATION
See Figures 1, 2, 3, 4, 5 and 6
Rough idle, hard starting, frequent engine miss at high speeds and physical deterioration are all indications that the plugs should be replaced.
The electrode end of a spark plug is a good indicator of the internal condition of your car's engine. If a spark plug is fouled, causing the engine to misfire, the problem will have to be found and corrected. Often, "reading'' the plugs will lead you to the cause of the problem.
A small amount of light tan or rust red colored deposits at the electrode end of the plug is normal. These plugs need not be renewed unless they are severely worn.
- Before removing the spark plugs, number the plug wires so that the correct wire goes on the plug when replaced. This can be done with pieces of adhesive tape.
- Next, clean the area around the plugs by brushing or blowing with compressed air.
- Disconnect the plug wires by twisting and pulling on the rubber cap, not on the wire.
- Remove each plug with a rubber-insert spark plug socket. Make sure that the socket is all the way down on the plug to prevent it from slipping and cracking the porcelain insulator.
- After removing each plug, evaluate its condition. A spark plug's useful life is approximately 30,000 miles (48,270 km) with electronic ignition. Thus, it would make sense to replace a plug if it has been in service that long. If the plug is to be replaced, install RN14MC5-3.3L engines and RC12LYC-3.5L engines. The numbers indicate heat range; hotter running plugs have higher numbers.
- If the plugs are to be reused, file the center and side electrodes flat with a fine, flat point file. Heavy or baked on deposits can be carefully scraped off with a small knife blade or the scraper tool on a combination spark plug tool. It is often suggested that plugs be tested and cleaned on a service station sandblasting machine; however, this piece of equipment is becoming rare. Check the gap between the electrodes with a round wire spark plug gapping gauge. Do not use a flat feeler gauge; it will give an inaccurate reading. If the gap is not as specified, use the bending tool on the spark plug gap gauge to bend the outside electrode. Be careful not to bend the electrode too far or too often, because excessive bending may cause the electrode to break off and fall into the combustion chamber. This would require removing the cylinder head to reach the broken piece and could also result in cylinder wall, piston ring, or valve damage.
- Clean the threads of old plugs with a wire brush. Lubricate the threads with a drop of oil.
- Screw the plugs in finger-tight, and then tighten them with the spark plug socket to 20 ft. lbs. (28 Nm). Be very careful not to overtighten them.
- Reinstall the wires. If, by chance, you have forgotten to number the plug wires, refer to the firing order illustrations.
INSPECTION & GAPPING
See Figures 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16
Check the plugs for deposits and wear. If they are not going to be replaced, clean the plugs thoroughly. Remember that any kind of deposit will decrease the efficiency of the plug. Plugs can be cleaned on a spark plug cleaning machine, which can sometimes be found in service stations, or you can do an acceptable job of cleaning with a stiff brush. If the plugs are cleaned, the electrodes must be filed flat. Use an ignition points file, not an emery board or the like, which will leave deposits. The electrodes must be filed perfectly flat with sharp edges; rounded edges reduce the spark plug voltage by as much as 50%.
Check spark plug gap before installation. The ground electrode (the L-shaped one connected to the body of the plug) must be parallel to the center electrode and the specified size wire gauge (please refer to the Tune-Up Specifications chart for details) must pass between the electrodes with a slight drag.
NEVER adjust the gap on a used platinum type spark plug.
Always check the gap on new plugs as they are not always set correctly at the factory. Do not use a flat feeler gauge when measuring the gap on a used plug, because the reading may be inaccurate. A round-wire type gapping tool is the best way to check the gap. The correct gauge should pass through the electrode gap with a slight drag. If you're in doubt, try one size smaller and one larger. The smaller gauge should go through easily, while the larger one shouldn't go through at all. Wire gapping tools usually have a bending tool attached. Use that to adjust the side electrode until the proper distance is obtained. Absolutely never attempt to bend the center electrode. Also, be careful not to bend the side electrode too far or too often as it may weaken and break off within the engine, requiring removal of the cylinder head to retrieve it.