GM Lumina/Grand Prix/Cutlass Supreme/Regal 1988-1996

Spark Plugs

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See Figures 1 and 2

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 90ºangle 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.



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Fig. Fig. 1: Cross-section of a spark plug



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Fig. Fig. 2: 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 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 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



Remove the spark plugs and wires one at a time to avoid confusion and miswiring during installation.


WARNING
To avoid engine damage, do NOT remove spark plugs when the engine is warm; the spark plug threads may be stripped if removed on a hot engine.

2.2L Engine
  1. Disconnect the negative battery cable. If the vehicle has been run recently, allow the engine to thoroughly cool.
  2.  
  3. 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.
  4.  
  5. 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.
  6.  

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.

  1. 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.
  2.  


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.

To install:
  1. Inspect the spark plug boot for tears or damage. If a damaged boot is found, the spark plug wire must be replaced.
  2.  
  3. 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.
  4.  
  5. Carefully thread 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 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.
  6.  


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 cross-threading and damaging the cylinder head bore.

  1. 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 specifications provided by the vehicle or plug manufacturer.
  2.  
  3. 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.
  4.  

2.3L Engine

See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: The ignition coil and module assembly must be removed to gain access to the spark plugs on the 2.3L engine

The spark plugs on this engine are located under the ignition coil and module assembly. To gain access to the spark plugs, the coil and module assembly must be removed.

  1. Remove the air cleaner assembly.
  2.  
  3. Disconnect the negative battery cable. If the vehicle has been run recently, allow the engine to thoroughly cool.
  4.  
  5. Detach the ignition coil cover electrical connector.
  6.  
  7. Unfasten the four ignition cover-to-cylinder head bolts.
  8.  
  9. If any of the boots stick to the spark plug, use a spark plug connector removing tool J-36011 or equivalent to remove the boot using a twisting motion.
  10.  
  11. Remove the ignition cover and set aside.
  12.  
  13. Clean any dirt away from the spark plug recess area, then remove the spark plugs using a suitable spark plug socket.
  14.  

To install:
  1. 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.
  2.  
  3. Carefully thread 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 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.
  4.  


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 cross-threading and damaging the cylinder head bore.

  1. Tighten the plugs to 17 ft. lbs. (23 Nm).
  2.  
  3. If removed, install the plug boots and retainers-to-ignition cover.
  4.  
  5. Apply a suitable silicone dielectric compound to the plug boot.
  6.  
  7. Install the ignition cover-to-engine while carefully aligning the boots with the spark plug terminals.
  8.  
  9. Apply thread locking compound Loctite®or equivalent to the ignition cover bolts. Install the bolts and tighten to 15 ft. lbs. (20 Nm).
  10.  
  11. Attach the ignition cover electrical connectors.
  12.  
  13. Connect the negative battery cable, then install the air cleaner.
  14.  

2.5L Engine
  1. Disconnect the negative battery cable. If the vehicle has been run recently, allow the engine to thoroughly cool.
  2.  
  3. Remove air cleaner components in order to gain access to the spark plugs.
  4.  
  5. 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.
  6.  
  7. 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.
  8.  

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.

  1. 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.
  2.  


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.

To install:
  1. 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.
  2.  
  3. Carefully thread 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 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.
  4.  


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 cross-threading and damaging the cylinder head bore.

  1. Tighten the spark plug to 20 ft. lbs. (27 Nm).
  2.  
  3. Fasten the cable on the plug, making sure it snaps into place. Repeat for the remaining spark plugs.
  4.  
  5. Install the air cleaner components.
  6.  
  7. Connect the negative battery cable.
  8.  

2.8L and 3.1L Engine

See Figures 4, 5 and 6



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Fig. Fig. 4: When removing the spark plug wires, pull on the boot, NOT on the wire itself



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Fig. Fig. 5: Use a socket and suitable extension...



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Fig. Fig. 6: ... then remove the spark plug from the cylinder head

In order to gain access to the spark plugs, the engine must first be rotated.

  1. Disconnect the negative battery cable. If the vehicle has been run recently, allow the engine to thoroughly cool.
  2.  
  3. For vehicles through 1994, rotate the engine as follows:
    1. Place the transaxle in Neutral.
    2.  
    3. Remove the air cleaner assembly and coolant recovery bottle.
    4.  
    5. Unfasten the torque strut-to-engine bracket bolts and swing the torque struts aside.
    6.  
    7. Replace the passenger side torque strut-to-engine bracket bolt in the engine bracket.
    8.  
    9. Position a prybar in the bracket so that it contacts the bracket and the bolt.
    10.  
    11. Rotate the engine by pulling forward on the prybar.
    12.  
    13. Align the slave hole in the driver side torque strut to the engine bracket hole.
    14.  
    15. Retain the engine in this position using the torque strut-to-engine bracket bolt.
    16.  

    1. Place the transaxle in Neutral.
    2.  
    3. Remove the air cleaner assembly and coolant recovery bottle.
    4.  
    5. Unfasten the torque strut-to-engine bracket bolts and swing the torque struts aside.
    6.  
    7. Install engine tilter J 41131 or equivalent, then rotate the engine forward.
    8.  

  4.  
  5. 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.
  6.  
  7. 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.
  8.  

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.

  1. 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.
  2.  


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.

To install:
  1. 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.
  2.  
  3. Carefully thread 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 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.
  4.  


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 cross-threading and damaging the cylinder head bore.

  1. Tighten the spark plug to 18 ft. lbs. (24 Nm). Install the cable on the plug. Make sure it snaps in place.
  2.  
  3. Repeat for the remaining spark plugs.
  4.  
  5. For vehicles through 1994, proceed as follows to bring the engine back to its original position:
    1. To bring the engine back into position, pull forward on the prybar to relieve the engine's weight. Then remove the driver side torque strut-to-engine bracket bolt from the torque strut slave hole and engine bracket.
    2.  
    3. Allow the engine to rotate back to its original position.
    4.  
    5. Remove the prybar.
    6.  
    7. Remove the passenger side torque strut-to-engine bracket bolt from the bracket.
    8.  
    9. Install the torque struts and strut-to-engine bracket bolts. Torque the bolts to 51 ft. lbs. (70 Nm).
    10.  
    11. Put the transaxle inPark.
    12.  

    1. Rotate the engine backward, then remove J 41131.
    2.  
    3. Fasten the torque strut-to-engine bracket bolts.
    4.  
    5. Put the transaxle inPark.
    6.  

  6.  
  7. Install the coolant recovery bottle and air cleaner assembly.
  8.  
  9. Connect the negative battery cable.
  10.  

3.4L Engine
  1. Disconnect the negative battery cable. If the vehicle has been run recently, allow the engine to thoroughly cool.
  2.  
  3. If necessary for access, remove the upper intake manifold, as outlined in Engine & Engine Overhaul of this repair guide.
  4.  
  5. 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.
  6.  
  7. 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.
  8.  

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.

  1. 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.
  2.  


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.

  1. Tag the spark plug wires to avoid confusion during installation.
  2.  
  3. Disconnect the spark plug wire by pulling and twisting the boot; then remove the spark plug.
  4.  

To install:
  1. 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.
  2.  
  3. Carefully thread 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 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.
  4.  


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 cross-threading and damaging the cylinder head bore.

  1. Tighten the spark plugs to 18 ft. lbs. (24 Nm).
  2.  
  3. Fasten the spark plug wire on the plug, as tagged during removal. Make sure it snaps in place.
  4.  
  5. Repeat for the remaining spark plugs.
  6.  
  7. Connect the negative battery cable.
  8.  

3.4L Engine

See Figure 7



Click image to see an enlarged view

Fig. Fig. 7: When installing the heat shields, make sure they are seated against the bump stop and the lower tabs extend over the plug's hex

  1. Disconnect the negative battery cable. If the vehicle has been run recently, allow the engine to thoroughly cool.
  2.  
  3. Tag the spark plug wires to avoid confusion during installation. a turn 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.
  4.  
  5. On the right rear cylinders only, use tool J 38491, or equivalent small pry tool, to carefully pry the heat shields up from the spark plugs.
  6.  
  7. 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.
  8.  

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.

  1. 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.
  2.  


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.

To install:
  1. 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.
  2.  
  3. Carefully thread 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 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.
  4.  


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 cross-threading and damaging the cylinder head bore.

  1. Tighten the spark plugs to 20 ft. lbs. (27 Nm) for vehicles through 1991 and to 11 ft. lbs. (15 Nm) for 1992-96 vehicles.
  2.  
  3. Install the heat shields. When installing the heat shields, make sure they are seated against the bump stop and the lower tabs extend over the spark plug's hex.
  4.  

  1. Connect the negative battery cable.
  2.  

GAPPING



See Figures 8 through 15



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Fig. Fig. 8: A normally worn spark plug should have light tan or gray deposits on the firing tip



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Fig. Fig. 9: A variety of tools and gauges are needed for spark plug service



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Fig. Fig. 10: A carbon fouled plug, identified by soft, sooty, black deposits, may indicate an improperly tuned vehicle. Check the air cleaner, ignition components and engine control system



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Fig. Fig. 11: Checking the spark plug gap with a feeler gauge



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Fig. Fig. 12: A physically damaged spark plug may be evidence of severe detonation in that cylinder. Watch that cylinder carefully between services, as a continued detonation will not only damage the plug, but could also damage the engine



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Fig. Fig. 13: Adjusting the spark plug gap



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Fig. Fig. 14: Used spark plugs which show damage may indicate engine problems



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Fig. Fig. 15: Inspect the spark plug to determine engine running conditions

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 wire type gapping tool is the best way to check the gap. 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.

 
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