Grand Cherokee 2WD Limited V8-4.7L (2002)
Spark Plug: Description and Operation
SPARK PLUGS
Both the 4.0L 6-cylinder and the 4.7L V-8 engine use resistor type spark plugs. Standard 4.7L V-8 engines are equipped with "fired in suppressor
seal" type spark plugs using a copper core ground electrode. High-Output (HO) 4.7L V-8 engines are equipped with unique plugs using a platinum
rivet located on the tip of the center electrode.
Because of the use of an aluminum cylinder head on the 4.7L engine, spark plug torque is very critical.
To prevent possible pre-ignition and/or mechanical engine damage, the correct type/heat range/number spark plug must be used. Do not substitute any
other spark plug on the 4.7L HO engine. Serious engine damage may occur.
Plugs on both engines have resistance values ranging from 6,000 to 20,000 ohms (when checked with at least a 1000 volt spark plug tester). Do not
use an ohmmeter to check the resistance values of the spark plugs. Inaccurate readings will result.
Remove the spark plugs and examine them for burned electrodes and fouled, cracked or broken porcelain insulators. Keep plugs arranged in the order
in which they were removed from the engine. A single plug displaying an abnormal condition indicates that a problem exists in the corresponding
cylinder.
EXCEPT 4.7L HO ENGINE
Spark plugs that have low mileage may be cleaned and reused if not otherwise defective, carbon or oil fouled. Also refer to Spark Plug Conditions.
Never clean spark plugs on the 4.7L HO engine. Damage to the platinum rivet will result.
CAUTION: Never use a motorized wire wheel brush to clean the spark plugs. Metallic deposits will remain on the spark plug insulator and will cause
plug misfire.
Fig.24 Plug Gap - 4.7L HO
HO Gap Adjustment: If equipped with the 4.7L HO engine, do not use a wire-type gapping tool as damage to the platinum rivet on the center
electrode may occur. Use a tapered-type gauge.
