GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Spark Plugs

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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 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

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 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.



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Fig. Fig. 2: Spark plug heat range

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



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. In normal operation plug gap increases about 0.001 inch (0.025mm) for every 2500 miles (4000 km). On the some engines, the spark plugs are platinum and require replacement every 100,000 miles (160,900 km) or 60 months which ever comes first. 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 will drop as the gap widens (along with fuel economy and power).

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.

Except 2.3L Engine (VIN A, D, and 3) and 2.4L (VIN T) See Figures 3 and 4

  1. Disconnect the negative battery cable, and if the vehicle has been run recently, allow the engine to thoroughly cool.
  2.  
  3. On some models it may be necessary to remove the air cleaner or any other components hindering spark plug removal.
  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.  



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Fig. Fig. 3: Remove the spark plug wire by twisting the boot 1/2turn, then pulling up

  1. 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.
  2.  

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.  



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Fig. Fig. 4: Using the proper size socket and ratchet combination, remove the spark plugs


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.  

The spark plug gap is sometimes embossed on the valve cover.

  1. 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, 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.
  2.  


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.

  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 /4turn to crush the washer. If you are installing a tapered seat plug, tighten the plug to specifications as follows:
  2.  



2.0L (VIN M) engine 20 ft. lbs. (27 Nm)
 
2.3L QUAD 15-18 ft. lbs. (21-28 Nm)
 
2.5L (VIN U) engine 15 ft. lbs. (21 Nm)
 
3.0L (VIN L) and 3.3L (VIN N) engines 11 ft. lbs. (15 Nm)
 
3.1L (VIN M) 13 ft. lbs. (18 Nm)
 

  1. 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.
  2.  

2.3L Engine (VIN A, D, and 3) and 2.4L (VIN T) See Figures 5, 6, 7 and 8

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. On the 2.3L (VIN D) and 2.4L (VIN T) engines, the spark plugs are platinum and require replacement every 100,000 miles (160,900 km) or 60 months which ever comes first.

To avoid engine damage, do not remove the spark plugs when the engine is warm. When you're removing spark plugs, work on only 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. The best location for numbering is as near as possible to the spark plug boot.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the 4 bolts retaining the Integrated Direct Ignition (IDI) or Electronic Ignition (EI) coil/module/cover assembly (depending upon vehicle application), then detach the electrical connector. Remove the assembly by pulling it straight up away from the engine.
  4.  



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Fig. Fig. 5: To remove the cover, unfasten the four bolts, then pull the assembly straight up from the engine

  1. If the connector(s) sticks to the spark plug, use spark plug connector removing tool J-36011 or equivalent, and a twisting motion to detach the connector(s) from the plugs.
  2.  



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Fig. Fig. 6: If any of the connectors stick to the spark plug, using this tool and a twisting motion will free the connectors from the spark plugs



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Fig. Fig. 7: Remove the four spark plug rubber covers

  1. Clean any dirt away from the spark plug recess area.
  2.  
  3. Remove the spark plug using the proper size socket, extensions and universal joints, as necessary. Hold the socket or the extension close to the plug with your free hand, as this will help lessen the possibility of applying a shear force which might snap the plug in half.
  4.  



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Fig. Fig. 8: Use a spark plug socket and remove each plug one at a time

To install:
  1. Lubricate the threads lightly with an anti-seize compound, then start the four spark plugs by hand. Tighten the plugs on the 2.3L (VIN A and 3) to 17 ft. lbs. (23 Nm) and on the 2.3L (VIN D ) and 2.4L (VIN T) tighten to 14 ft. lbs. (19 Nm).
  2.  
  3. If removed, install any the plug boot connectors that may have stuck to a spark plug to the IDI assembly.
  4.  

Check to make sure the spring terminal is inside the boot.

  1. Install the IDI or EI coil/module/cover assembly to the engine, while carefully aligning the boots with the spark plug terminals, by pushing the assembly straight down.
  2.  
  3. Apply Loctitethread locking compound, or equivalent to the cover bolts. Install the bolts and tighten to 2.3L (VIN A and 3) 13 ft. lbs. (18 Nm) and on the 2.3L (VIN D ) and 2.4L (VIN T) tighten to 16 ft. lbs. (22 Nm).
  4.  
  5. If removed, engage the ignition cover electrical connectors.
  6.  
  7. Connect the negative battery cable.
  8.  

INSPECTION & GAPPING



See Figures 9 through 13

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.



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Fig. Fig. 9: Inspect the spark plug to determine engine running conditions



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Fig. Fig. 10: A variety of tools and gauges are needed for spark plug service



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



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Fig. Fig. 12: Adjusting the spark plug gap



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Fig. Fig. 13: If the standard plug is in good condition, the electrode may be filed flat-WARNING: do not file platinum plugs

 
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