Spark Plug (Resistor, Platinum), 2007-2011 Wrangler (3.8L). Is your Jeep running rough? Changing the spark plugs will usually help it run better. Over time the electrode will erode causing a larger spark gap. Spark plugs are usually easy to replace. Get high quality replacement spark plugs to keep your Jeep running smooth. It may even help your gas mileage.