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    GM Century/Lumina/Grand Prix/Intrigue 1997-2000

    Spark Plugs

    Print

    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 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 HEAT RANGE





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    Fig. Cross-section of a typical spark plug



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    Fig. Spark plug heat range



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



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    Fig. Inspect the spark plug to determine engine running conditions

    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.

    The vehicles covered by this guide use resistor type, tapered seat spark plugs on all engines. No gasket is used on these tapered seat plugs. When replacing the spark plugs, use only the type specified.

    REMOVAL & INSTALLATION



    A set of spark plugs usually requires replacement after about 20,000-30,000 miles (32,000-48,000 km), depending on your style of driving. Top quality (platinum) plugs in a well-maintained engine may go as many as 100,000 miles (160,000 km) between change intervals. On some engines, hard parts such as the intake manifold may need to be disassembled. On V6 engines, the firewall side spark plugs will be difficult access, so spark plug changes have become more of challenge than in times past, another reason manufacturers have gone to longer change intervals. On a practical note, many technicians feel that letting spark plugs stay in the engine that long will make removal very difficult and may even damage the cylinder head, especially aluminum heads.



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    Fig. Although the original spark plug wires may have identification numbers on them, it is good practice to use small tags to identify the spark plug wires before removal, to avoid improper installation



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    Fig. A flex-head ratchet, along with a suitable extension and spark plug socket help with spark plug removal and installation



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    Fig. The small protrusions on this spark plug's electrodes identify it as a platinum tipped spark plug that can be regapped but must not be filed or the platinum tips will be damaged



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    Fig. For spark plugs being installed in cast iron cylinder heads, apply a small amount of clean engine oil to the spark plug threads



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    Fig. For spark plugs being installed in aluminum cylinder heads, it is important to apply a small amount of anti-seize compound to the spark plug threads



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    Fig. It can be hard to start the threads, so slip a piece of tight-fitting vacuum hose over the end of the spark plugs, then install the plug, turning with the hose



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    Fig. This spark plug wire has a heat shield

    Some sources feel, that 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 may drop as the gap widens (along with fuel economy and power).

    There are a number of points to keep in mind when changing spark plugs.



    When you're 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. If the vehicle has been run recently, allow the engine to thoroughly cool.
     
    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, 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. Use a spark plug socket that is equipped with a rubber insert to properly hold the plug.
     


    WARNING
    Be sure not to use a flexible extension on the socket. Use of a flexible extension may allow a shear force to be applied to the plug. A shear force could break the plug off in the cylinder head, leading to costly and frustrating repairs.



    Use care when threading the plug 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.
     


    WARNING
    Do not use the spark plug socket to thread the plugs. Always carefully thread the plug by hand or using an old plug wire to prevent the possibility of crossthreading and damaging the cylinder head bore.



    Use care when tightening the spark plug. The vehicles covered by this guide all use tapered seat plugs. They do not require as much torque as plugs with crush gaskets. Tighten the plug to specifications provided by the vehicle or plug manufacturer. GM original equipment spark plug wires have a coating on them and GM no longer recommends putting silicone dielectric compound on the end of the spark plug lead or inside the spark plug boot to prevent sticking, since they feel this leaks to carbon tracking and spark plug misfire. Carefully 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.
     

    3.1L (VIN M) Engines
    1. Turn the ignition switch to the OFF position, then disconnect the negative battery cable..
    2.  
    3. Remove only one spark plug wire at a time to avoid mixing up the wires. Each must be returned to its original location. Note the position of the spark plug wires before removing them. The high energy in these ignition systems can cause induced voltages to fire in adjacent spark plug wires. For this reason, the factory engineers take care to position the wires to minimize "crossfire." Wires should be returned to their exact locations and secured with whatever clips or loom components were originally installed.
    4.  
    5. Spark plug boots tend to stick firmly to the spark plug insulator. DO NOT pull on the spark plug wire. Pull on the spark plug boot or heat shield only, twisting a half-turn to release the seal while removing. Do not pull on the spark plug wire or it may be damaged.
    6.  
    7. Using the proper size spark plug socket, remove the plug from the cylinder head.
    8.  



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    Fig. When removing the spark plug wires, pull on the boot, NOT on the wire itself



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    Fig. Use a socket and suitable extension . . .



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    Fig. . . . then remove the spark plug from the cylinder head

    To install:

    1. Verify that the spark plug is clean, properly gapped and that the threads are lightly lubricated with clean engine oil.
    2.  
    3. Be sure the plug threads smoothly into the cylinder head and is fully seated. Use a "thread chaser" if necessary to clean the threads in the cylinder head. Cross-threading or failing to fully seat the spark plug can cause overheating of the plug, exhaust blow-by, or thread damage. Follow the recommended torque specifications carefully. Some technicians will place a small piece of rubber tubing (like a piece of vacuum line) on the terminal end of the spark plug and use it to turn the plug, by hand. In this way, if the plug is not threaded properly, not enough torque can be placed on the plug to do any damage, especially on engines such as the 3.1L that have aluminum heads.
    4.  
    5. Torque the spark plug to 11-15 ft. lbs. (15-20 Nm).
    6.  
    7. Install the spark wire to the spark plug, making sure the connector engages the spark plug and the boot is fully seated.
    8.  

    3.8L (VIN 1 and K) Engines


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    Fig. The cosmetic/acoustic engine cover must be removed for access to the spark plugs-3.8L engine

    1. Turn the ignition switch to the OFF position, then disconnect the negative battery cable.
    2.  
    3. On the 3.8L (VIN K) engine, the cosmetic/acoustic engine cover, also called the fuel injector sight shield, must be removed. Remove this cover by first turning the tube/oil fill cap counter-clockwise from the valve rocker arm cover. Lift the fuel injector sight shield up at the front and slide the tab out of the engine bracket.
    4.  
    5. Remove only one spark plug wire at a time to avoid mixing up the wires. Each must be returned to its original location. Note the position of the spark plug wires before removing them. The high energy in these ignition systems can cause induced voltages to fire in adjacent spark plug wires. For this reason, the factory engineers take care to position the wires to minimize "crossfire." Wires should be returned to their exact locations and secured with whatever clips or loom components were originally installed.
    6.  
    7. Spark plug boots tend to stick firmly to the spark plug insulator. DO NOT pull on the spark plug wire. Pull on the spark plug boot or heat shield only, twisting a half-turn to release the seal while removing. Do not pull on the spark plug wire or it may be damaged.
    8.  
    9. Using the proper size spark plug socket, remove the plug from the cylinder head.
    10.  

    To install:

    1. Verify that the spark plug is clean, properly gapped and that the threads are lightly lubricated with clean engine oil.
    2.  
    3. Be sure the plug threads smoothly into the cylinder head and is fully seated. Use a "thread chaser" if necessary to clean the threads in the cylinder head. Cross-threading or failing to fully seat the spark plug can cause overheating of the plug, exhaust blow-by, or thread damage. Follow the recommended torque specifications carefully. Some technicians will place a small piece of rubber tubing (like a piece of vacuum line) on the end of the spark plug and use it to turn the plug, by hand. In this way, if the plug is not threaded properly, not enough torque can be placed on the plug to do any damage.
    4.  
    5. Torque the spark plug to 11-15 ft. lbs. (15-20 Nm).
    6.  
    7. Install the spark wire to the spark plug, making sure the connector engages the spark plug and the boot is fully seated.
    8.  
    9. On the 3.8L (VIN K) engine, install the cosmetic/acoustic cover. Insert the tab of the fuel injector sight shield under the engine bracket. Place the hole of the shield onto the oil fill neck of the valve rocker arm cover. Install the tube/oil fill cap onto the valve rocker arm cover and twist clockwise in order to lock.
    10.  

    3.4L (VIN X) Engine
    1. Disconnect the negative battery cable.
    2.  
    3. Turn the ignition switch to the OFF position.
    4.  
    5. Remove the upper intake manifold, as outlined in of this guide.
    6.  
    7. Remove only one spark plug wire at a time to avoid mixing up the wires. Each must be returned to its original location. Note the position of the spark plug wires before removing them. The high energy in these ignition systems can cause induced voltages to fire in adjacent spark plug wires. For this reason, the factory engineers take care to position the wires to minimize "crossfire." Wires should be returned to their exact locations and secured with whatever clips or loom components were originally installed.
    8.  
    9. Spark plug boots tend to stick firmly to the spark plug insulator. DO NOT pull on the spark plug wire. Pull on the spark plug boot or heat shield only, twisting a half-turn to release the seal while removing. Do not pull on the spark plug wire or it may be damaged.
    10.  
    11. Using the proper size spark plug socket, remove the plug from the cylinder head.
    12.  

    To install:

    1. Verify that the spark plug is clean, properly gapped and that the threads are lightly lubricated with clean engine oil.
    2.  
    3. Be sure the plug threads smoothly into the cylinder head and is fully seated. Use a "thread chaser" if necessary to clean the threads in the cylinder head. Cross-threading or failing to fully seat the spark plug can cause overheating of the plug, exhaust blow-by, or thread damage. Follow the recommended torque specifications carefully. Some technicians will place a small piece of rubber tubing (like a piece of vacuum line) on the end of the spark plug and use it to turn the plug, by hand. In this way, if the plug is not threaded properly, not enough torque can be placed on the plug to do any damage, especially on engines with aluminum heads such as the 3.4L.
    4.  
    5. Torque the spark plug to 11-15 ft. lbs. (15-20 Nm).
    6.  
    7. Install the spark wire to the spark plug, making sure the connector engages the spark plug and the boot is fully seated.
    8.  
    9. Install the upper intake manifold. Please refer to .
    10.  

    3.5L (VIN H) Engine

    This procedure requires the removal of the engine cosmetic/acoustic cover and the removal of the ignition coil assembly. This engine does not use spark plug wires. The ignition coils plug onto the spark plug tops.



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    Fig. On the 3.5L engine, the spark plugs are located directly under the ignition coil "cassette". No spark plug wires are used

    1. Turn the ignition switch to the OFF position. The engine must be cool before removing the spark plugs. Attempting to remove the spark plugs from a hot engine may cause the plug threads to seize, causing damage to the cylinder head threads.
    2.  
    3. Remove the ignition coil assembly. For this procedure, please refer to .
    4.  
    5. Remove the spark plug boots from the plugs using GM tool J 43094, or an equivalent tool. GM specifically warns against using pliers or other makeshift tools to remove the spark plug boots.
    6.  
    7. Clean the spark plug recess area before removing the spark plugs. Failure to do so could result in engine damage because of dirt or foreign material entering the cylinder head, or by contamination of the cylinder head threads. The contaminated threads may prevent the proper seating of the new plug. Use a thread chaser to clean the threads of any contamination.
    8.  
    9. Remove the spark plugs from the engine.
    10.  

    To install:

    1. Use only the spark plugs specified for use in this vehicle. Do not install spark plugs that are either hotter or colder than those specified for the vehicle. Installing spark plugs of another type can severely damage the engine.
    2.  
    3. Check the gap of all new and reconditioned spark plugs before installation. The pre-set gaps may have changed during handling. Use a round feeler gauge to ensure an accurate check. Installing the spark plugs with the wrong gap can cause poor engine performance and may even damage the engine.
    4.  
    5. Use care installing the spark plugs. Be sure the spark plugs thread smoothly into the cylinder heads and that the spark plug is fully seated. Cross-threading or failing to fully seat the spark plug can cause overheating of the plug, exhaust blow-by, or thread damage.
    6.  
    7. Tighten the spark plugs to 15 ft. lbs. (20 Nm).
    8.  
    9. Install the spark plug boots to the ignition coil assembly.
    10.  
    11. Install the ignition coil assembly following the procedure in .
    12.  

    INSPECTION & GAPPING



    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. These machines are small abrasive blasters and some authorities feel, that since it rounds off the edge of the electrode, it actually raises the voltage requirements to fire the spark plug. While you may be able to do an acceptable job of cleaning with a stiff brush, keep in mind that spark plugs are relatively inexpensive and if there is any question as to their condition, replace them. 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. A spark jumps better from a sharp edge

    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. 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.

    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 in the engine, likely burying itself in the relatively softer metal of the piston top the first time the engine is started.



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    Fig. Checking the spark plug gap with a round wire spark plug gauge



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    Fig. Adjusting the spark plug gap



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    Fig. If the standard plug is in good condition, the electrode may be filed flat-WARNING: do not file platinum plugs

     
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