GM Malibu/Cutlass 1997-2000

Spark Plugs

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Tapered seat spark plugs without gaskets are used on both engines. Both engines use a resistor type, platinum tip spark plug. Special procedures for platinum tipped spark plugs are to be followed.

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. Cross-section of a spark plug

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.



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Fig. 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. Occasional highway driving is recommended for good spark plug performance because of the increased combustion heat. This heat burns away any excess deposits that may have formed from frequent idling or stop and go driving.

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 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 will drop as the gap widens (along with fuel economy and power).


NOTE
Both the 2.4L and the 3.1L engine come equipped with factory installed platinum tipped spark plugs. Because of platinum's durability, the manufacturer does not suggest replacing the spark plugs for 100,000 miles(166,000 km), even in the most demanding conditions. When spark plugs are replaced, it is recommended they are replaced with platinum tipped spark plugs. Most platinum tipped spark plugs are factory gapped, and it is recommended that they not be re-gapped because the thin layer of platinum may be damaged. If necessary to gap platinum tip plugs, extreme care should be taken to not damage or misalign the electrodes.

2.4L 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.


NOTE
This engine has aluminum cylinder heads. Do not remove the spark plugs from a hot engine, allow it to cool first. Removing the spark plugs from a hot engine may cause spark plug thread damage or cylinder head damage. To avoid engine damage, do not remove the spark plugs when the engine is warm.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the 4 bolts retaining the electronic ignition coil/module/cover assembly, then detach the electrical connector. Remove the assembly by pulling it straight up away from the engine.
  4.  



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

  1. If any of the connector(s) sticks to the spark plug, use a spark plug connector removing tool or soft jawed pliers, and a twisting motion to detach the connector(s) from the plugs.
  2.  
  3. Remove the spark plug covers, as necessary.
  4.  



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Fig. 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. 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 spark plug 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. Use the proper sized spark plug socket to remove each plug one at a time

  1. Using a wire feeler gauge, check and, if not using platinum plugs, 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.  


NOTE
It is not recommended to gap factory gapped platinum type plugs.

To install:

  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 cross-thread
  2.  
  3. Tighten the plug to 13 ft. lbs. (18 Nm).
  4.  
  5. If removed, install any of the plug boot connectors that may have stuck to a spark plug.
  6.  


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

  1. Install the 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 Loctite®thread locking compound, or equivalent to the cover bolts. Install the bolts and 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.  

3.1L Engine


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Fig. These pliers protect the plug wire boot from being damaged during removal



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Fig. Connect the spark plug wires as shown in this routing diagram. The plug location and it's corresponding coil are indicated by numbers. Front of the 3.1L engine shown



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Fig. Attach the spark plug wires as shown in this routing diagram. The plug locations are indicated by numbers. Rear of the 3.1L engine shown



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Fig. During installation, make sure the spark plug wires are attached to their corresponding coil towers

  1. Disconnect the negative battery cable, and if the vehicle has been run recently, allow the engine to thoroughly cool.
  2.  


NOTE
This engine has aluminum cylinder heads. Do not remove the spark plugs from a hot engine, allow it to cool first. Removing the spark plugs from a hot engine may cause spark plug thread damage or cylinder head damage. To avoid engine damage, do not remove the spark plugs when the engine is warm.

  1. 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.
  2.  
  3. 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.
  4.  


NOTE
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. 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.  


NOTE
It is not recommended to gap factory gapped platinum type plugs.

To install:

  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 cross-thread.
  2.  


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

  1. Carefully tighten the spark plug to 13 ft. lbs. (18 Nm).
  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.  

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, 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.


NOTE
It is not recommended to adjust the gap on a used platinum type spark plug. NEVER clean platinum type plugs with a wire brush or file.

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. Inspect the spark plug to determine engine running conditions



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



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Fig. Checking the spark plug gap with a feeler 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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