GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

Spark Plugs

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See Figures 1, 2 and 3

Spark plugs ignite the air and fuel mixture in the cylinder as the piston reaches the top of the compression stroke. The controlled explosion that results forces the piston down, turning the crankshaft and the rest of the drive train.

The average life of a spark plug 30,000 miles (48,300 km). On the 2.2L (LN2),engine the life of the spark plug is 100,000 miles (166,000 km). Part of the reason for this extraordinarily long life is the exclusive use of unleaded fuel, which reduces the amount of deposits within the combustion chamber and on the spark plug electrodes themselves, compared with the deposits left by the leaded gasoline used in the past. An additional contribution to long life is made by the High Energy Ignition (HEI) system, which fires the spark plugs with over 35,000 volts of electricity. The high voltage serves to keep the electrodes clear, which suffer less pitting and wear compared to breaker point ignitions.



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Fig. Fig. 1: Breakdown of a common spark plug



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Fig. Fig. 2: Heat range on spark plugs explained

Nevertheless, the life of a spark plug is dependent on a number of factors, including the mechanical condition of the engine, driving conditions, and the driver's habits.

When you remove the plugs, check the condition of the electrodes, they are a good indicator of the internal state of the engine. Since the spark plug wires must be checked every 15,000 miles (24,000 km), the spark plugs can be removed and examined at the same time. This will allow you to keep an eye on the mechanical status of the engine.

A small deposit of light tan or rust/red material on a spark plug that has been used for any period of time is to be considered normal. Any other color, or abnormal amounts of wear or deposits, indicates that there is something amiss in the engine.



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Fig. Fig. 3: Explanation of the spark plugs numbering system

The gap between the center electrode and the side or ground electrode can be expected to increase not more than 0.001 in. (0.025mm) every 1000 miles (1609 km) under normal conditions.

When a spark plug is functioning normally or, more accurately, when the plug is installed in an engine that is functioning properly, the plugs can be taken out, cleaned, regapped, and reinstalled in the engine without doing the engine any harm.

When, and if, a plug fouls and begins to misfire, you will have to investigate, correct the cause of the fouling, and either clean or replace the plug.

There are several reasons why a spark plug will foul and you can learn which is at fault by just looking at the plug. A few of the most common reasons for plug fouling, and a description of the fouled plug's appearance, are listed in a picture in this section.

Spark plugs suitable for use in your car's engine are offered in a number of different heat ranges. The amount of heat which the plug absorbs is determined by the length of the lower insulator. The longer the insulator, the hotter the plug will operate; the shorter the insulator, the cooler it will operate. A spark plug that absorbs (or retains) little heat and remains too cool will accumulate deposits of oil and carbon, because it is not hot enough to burn them off. This leads to fouling and consequent misfiring. A spark plug that absorbs too much heat will have no deposits, but the electrodes will burn away quickly and, in some cases, pre-ignition may result. Pre-ignition occurs when the spark plug tips get so hot that they ignite the fuel/mixture before the actual spark fires. This premature ignition will usually cause a pinging sound under conditions of low speed and heavy load. 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. In this case, the resultant explosion (detonation) will be strong enough to damage pistons, rings, and valves.

In most cases, the factory recommended heat range is correct; it is chosen to perform well under a wide range of operating conditions. However, if most of your driving is long distance, high speed travel, you may want to install a spark plug one range colder than standard. If most of your driving is of the short trip variety, when the engine may not always reach operating temperature, a hotter plug may help burn off the deposits normally accumulated under those conditions.

REMOVAL & INSTALLATION



See Figures 4, 5, 6, 7, 8, 9, 10, 11 and 12

Before you replace your spark plugs make sure your engine is cool. If you do attempt to remove the plugs on a hot engine, several things could occur. The spark plugs could seize, causing damage to the cylinder head threads which can be expensive. You can also burn yourself severely. Also, make sure you clean the recess area thoroughly before removing the plugs. Any dirt entering the plug area will prevent the plug not to seat properly.

  1. Number the wires with pieces of adhesive tape so that you won't cross them when you replace them.
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  3. The spark plug boots have large grips to aid in removal. Grasp the wire by the rubber boot and twist the boot 1 / 2 turn in either direction to break the tight seal between the boot and the plug. Then twist and pull on the boot to remove the wire from the spark plug. Do not pull on the wire itself or you will damage the carbon cord conductor.
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  5. Some of the engines may have a plug that is difficult to access. This requires the use of a special tool to aid in the removal and installation. There are two tools which are made for these kinds of problems: J-38491, to prevent damage to the wire by breaking the plug/boot bond, J-39294, to remove the plug wire from the rear bank of the engine.
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Fig. Fig. 4: Tool J-38491



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Fig. Fig. 5: Tool J -39294

  1. If compressed air is available, apply it to the area around the spark plug holes. Otherwise, use a rag or a brush to clean the area. Doing this now will help from dirt entering into the plug chamber after removal.
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  3. Use a correct size spark plug socket to loosen all of the plugs about two turns. A universal joint installed at the socket end of the extension will ease the process. 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.
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Fig. Fig. 6: The correct size socket is VERY important. You do not want to strip plug and not be able to remove it. This could be an expensive plug replacement

  1. Remove the plugs by unscrewing them the rest of the way.
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Fig. Fig. 7: Spark plugs can be removed with your hands after you have loosened them enough



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Fig. Fig. 8: A variety of tools and gauges are needed for spark plug service

To install:
  1. Check and adjust the gap. This includes old and new plugs. Never rely on "pre-gapped" plugs. Also, use a wire gauge as opposed to a flat feeler gauge.
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  3. Lubricate the threads of the spark plugs with a drop of oil or a shot of silicone spray. Install the plugs and tighten them hand-tight. Take care not to cross-thread them.
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  5. Tighten the spark plugs with the socket. Do not apply the same amount of force you would use for a bolt; just snug them in. These spark plugs do not use gaskets, and over-tightening will make future removal difficult. If a torque wrench is available, tighten to 10-20 ft. lbs. (13-27 Nm).
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Fig. Fig. 9: Checking the spark plug gap with a feeler gauge



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Fig. Fig. 10: Replacing the plug wires is easy when you have taken the time to mark everything



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Fig. Fig. 11: Used spark plugs which show damage may indicate engine problems



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Fig. Fig. 12: Inspect the spark plug to determine engine running conditions

While over-tightening the spark plug is to be avoided, under-tightening is just as bad. If combustion gases leak past the threads, the spark plug will overheat and rapid electrode wear will result.

  1. Install the wires on their respective plugs. Make sure the wires are firmly connected. You will be able to feel them click into place. Spark plug wiring diagrams are in this section if you get into trouble.
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