Liberty, Wrangler 2006-2007

Spark Plugs

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Inspection



Cold Fouling/Carbon Fouling: Cold fouling is sometimes referred to as carbon fouling. The deposits that cause cold fouling are basically carbon. A dry, black deposit on one or two plugs in a set may be caused by sticking valves or defective spark plug cables. Cold (carbon) fouling of the entire set of spark plugs may be caused by a clogged air cleaner element or repeated short operating times (short trips).

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Fig. Cold fouling/carbon fouling spark plugs

Wet Fouling or Gas Fouling: A spark plug coated with excessive wet fuel or oil is wet fouled. In older engines, worn piston rings, leaking valve guide seals or excessive cylinder wear can cause wet fouling. In new or recently overhauled engines, wet fouling may occur before break-in (normal oil control) is achieved. This condition can usually be resolved by cleaning and reinstalling the fouled plugs.

Oil or Ash Encrusted: If one or more spark plugs are oil or oil ash encrusted, evaluate engine condition for the cause of oil entry into that particular combustion chamber.

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Fig. Oil or ash encrusted spark plug

Electrode Gap Bridging: Electrode gap bridging may be traced to loose deposits in the combustion chamber. These deposits accumulate on the spark plugs during continuous stop-and-go driving. When the engine is suddenly subjected to a high torque load, deposits partially liquefy and bridge the gap between electrodes. This short circuits the electrodes. Spark plugs with electrode gap bridging can be cleaned using standard procedures.

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Fig. Electrode gap bridging

Scavenger Deposits: Fuel scavenger deposits may be either white or yellow. They may appear to be harmful, but this is a normal condition caused by chemical additives in certain fuels. These additives are designed to change the chemical nature of deposits and decrease spark plug misfire tendencies. Notice that accumulation on the ground electrode and shell area may be heavy, but the deposits are easily removed. Spark plugs with scavenger deposits can be considered normal in condition and can be cleaned using standard procedures.

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Fig. Scavenger deposits

Chipped Electrode Insulator: A chipped electrode insulator usually results from bending the center electrode while adjusting the spark plug electrode gap. Under certain conditions, severe detonation can also separate the insulator from the center electrode. Spark plugs with this condition must be replaced.

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Fig. Chipped electrode insulator

Pre-Ignition Damage: Pre-ignition damage is usually caused by excessive combustion chamber temperature. The center electrode dissolves first and the ground electrode dissolves somewhat latter. Insulators appear relatively deposit free. Determine if the spark plug has the correct heat range rating for the engine. Determine if ignition timing is over advanced or if other operating conditions are causing engine overheating. (The heat range rating refers to the operating temperature of a particular type spark plug. Spark plugs are designed to operate within specific temperature ranges. This depends upon the thickness and length of the center electrodes porcelain insulator.)


CAUTION
If the engine is equipped with copper core ground electrode spark plugs, they must be replaced with the same type/number spark plug as the original. If another spark plug is substituted, pre-ignition will result.



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Fig. Pre-ignition damage

Spark Plug Overheating: Overheating is indicated by a white or gray center electrode insulator that also appears blistered. The increase in electrode gap will be considerably in excess of 0.001 inch per 2000 miles of operation. This suggests that a plug with a cooler heat range rating should be used. Over advanced ignition timing, detonation and cooling system malfunctions can also cause spark plug overheating.


CAUTION
If the engine is equipped with copper core ground electrode spark plugs, they must be replaced with the same type/number spark plug as the original. If another spark plug is substituted, pre-ignition will result.



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Fig. Spark plug overheating

Removal & Installation



2.4L Engine

NOTE
If spark plug for No. 2 or No. 3 cylinder is being removed, throttle body must be removed.

  1. Remove air cleaner tube and housing.
  2.  
  3. Twist secondary cable at cylinder head to break loose at spark plug. Remove cable from plug.
  4.  
  5. Prior to removing spark plug, spray compressed air into cylinder head opening. This will help prevent foreign material from entering combustion chamber.
  6.  
  7. Remove spark plug from cylinder head using a quality socket with a rubber or foam insert.
  8.  
  9. Inspect spark plug condition.
  10.  

To install:


CAUTION
Spark plug tightening on the 2.4L is torque critical. The plugs are equipped with tapered seats. Do not exceed 15 ft. lbs. (20 Nm) torque.

  1. Special care should be taken when installing spark plugs into the cylinder head spark plug wells. Be sure the plugs do not drop into the plug wells as electrodes can be damaged.
  2.  
  3. Always tighten spark plugs to the specified torque. Over tightening can cause distortion resulting in a change in the spark plug gap or a cracked porcelain insulator.
  4.  
  5. Start the spark plug into the cylinder head by hand to avoid cross threading.
  6.  
  7. Tighten spark plugs.
  8.  
  9. Install throttle body.
  10.  
  11. Install air cleaner tube and housing.
  12.  

3.7L Engine

NOTE
Each individual spark plug is located under each ignition coil. Each individual ignition coil must be removed to gain access to each spark plug

  1. Prior to removing ignition coil, spray compressed air around coil base at cylinder head.
  2.  
  3. Prior to removing spark plug, spray compressed air into cylinder head opening. This will help prevent foreign material from entering combustion chamber.
  4.  
  5. Remove spark plug from cylinder head using a quality socket with a rubber or foam insert. Also check condition of ignition coil O-ring and replace as necessary.
  6.  
  7. Inspect spark plug condition.
  8.  

To install:


NOTE
Special care should be taken when installing spark plugs into the cylinder head spark plug wells. Be sure the plugs do not drop into the plug wells as electrodes can be damaged.


NOTE
Always tighten spark plugs to the specified torque. Over tightening can cause distortion resulting in a change in the spark plug gap or a cracked porcelain insulator.

  1. Start the spark plug into the cylinder head by hand to avoid cross threading.
  2.  
  3. Tighten spark plugs.
  4.  
  5. Before installing coil(s), check condition of coil O-ring and replace as necessary. To aid in coil installation, apply silicone to coil O-ring.
  6.  
  7. Install ignition coil(s).
  8.  

4.0L Engine

NOTE
On the 4.0L 6-cylinder engine the spark plugs are located below the coil rail assembly.

  1. Prior to removing the spark plug, spray compressed air around the spark plug hole and the area around the spark plug. This will help prevent foreign material from entering the combustion chamber.
  2.  
  3. Remove the spark plug using a quality socket with a rubber or foam insert.
  4.  
  5. Inspect the spark plug condition.
  6.  

To install:

  1. Always tighten spark plugs to the specified torque. Over tightening can cause distortion. This may result in a change in the spark plug gap, or a cracked porcelain insulator.
  2.  
  3. When replacing the spark plug and ignition coil cables, route the cables correctly and secure them in the appropriate retainers. Failure to route the cables properly can cause the radio to reproduce ignition noise. It could cause cross ignition of the spark plugs, or short circuit the cables to ground.
  4.  
  5. Start the spark plug into the cylinder head by hand to avoid cross threading.
  6.  
  7. Tighten the spark plugs to 26-30 ft. lbs. (35-41 Nm) torque.
  8.  
  9. Install coil rail.
  10.  

 
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