Edmunds Answers



  • karjunkie 05/23/10 10:01 am PST

    Jeep Grand Cherokee spark plugs need to be changed every 30,000 to 60,000 miles. The coils do not need any periodic replacement. They are good for life unless one or more go bad. On the 4.7 liter engine, the spark plugs are located under each corresponding engine coil. Make sure you use exactly the same type of spark plug specified by the manufacturer. Mopar SPRC12MCC4 gapped to 0.040 is the correct plug for your 4.7L V8 engine. You first need to disconnect the negative terminal on the battery and remove the throttle body resonator box and air duct which is held in place with 2 10 MM bolts. Then you disconnect and remove the coils to access the spark plugs removing one 10 MM bolt and the snap on electrical connector. Turn the coil/boot assembly a quarter turn back and forth to loosen the lock and then pull back on the boot frimly to remove the wire. Use a special spark plug socket, extension and wrench to remove the spark plug from the cylinder head. Turn the socket counter-clockwise to unscrew the spark plug. Spread anti-seize compound over the threads of the new spark plug. Anti-seize compound or equivalent lubricant is available at any auto parts store where you buy the plugs. Begin to manually screw the new spark plug into the cylinder head with just the socket and the extension. Finish tightening the spark plug with the wrench attached to the socket and extension. Check and adjust the tension on the spark plug. The appropriate amount of tension is listed on the plug's packaging. For your engine, the correct tension is 20 foot pounds. If you do not have a torque wrench install plugs snug with your hand and then turn 1/4 turn with the wrench. Place the spark plug wire's boot onto the spark plug. Turn it gently from side to side to lock the boot into place and then reconnect the coil.


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