Jeep Repair Problems? Ask a Mechanic for Answers ASAP
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On the 4.0L 6 - cylinder engine, the spark plugs are located below the coil rail assembly. On the 4.7L V - 8 engine, each individual spark plug is located under each ignition coil.
The plugs may be cleaned using commercially available spark plug cleaning equipment. After cleaning, file center electrode flat with a small point file or jewelers file before adjusting gap.
CAUTION: Never use a motorized wire wheel brush to clean spark plugs. Metallic deposits will remain on spark plug insulator and will cause plug misfire.
Check spark plug gap with a gap gauge tool. If the gap is not correct, adjust it by bending ground electrode (see picture)Never attempt to adjust gap by bending center electrode.
CAUTION: The 4.7L V - 8 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.
Special care should be taken when installing spark plugs into cylinder head spark plug wells. Be sure plugs do not drop into plug wells as ground straps may be bent resulting in a change in plug gap, or electrodes can be damaged.
Always tighten spark plugs to specified torque. Over tightening can cause distortion resulting in a change in spark plug gap or a cracked porcelain insulator.
A one-piece coil rail assembly containing three individual coils is used on the 4.0L engine The coil rail must be replaced as one assembly. The bottom of the coil is equipped with 6 individual rubber boots Ignition Coil Assembly - 4.0L 6 - Cylinder Engine to seal the 6 spark plugs to the coil. Inside each rubber boot is a spring. The spring is used for an electrical contact between the coil and the top of the spark plug. These rubber boots and springs are a permanent part of the coil and are not serviced separately.
The gap is .035 in.
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