It is the Jeep spark plug that ignites the contents in the combustion chamber. This is the final component in an ignition system which, if all parts are operating as expected, keeps the engine running smoothly. There is a Jeep spark plug for each cylinder in your engine. They all must not only be producing a spark, but also at the same level of intensity for the engine to operate normally. The split of the ignition system to the individual spark plugs originates at the coil on the newer vehicles and at the distributor on the older Jeeps. Because of the way the system is set up, if there is an uneven electrical discharge at one of the spark plugs as compared to the others, you can reasonably assume the problem is with either the plug or the ignition wire it is connected to. The proper diagnosis of this situation is done by testing the individual spark plugs and the wires on the Jeep engine. This is accomplished by pulling one of the plugs and reconnecting it to the wire. By grounding out the electrode of the plug to the engine, a spark can be seen while the engine is running. If the spark is not a strong blue flash, there is a problem with either the spark plug or the wire. By replacing one at a time the faulty component can be positively identified. Even when one component is found to be faulty, all of them should be tested just to make sure there is not more than one faulty part in your ignition system. Once the faulty ignition component is replaced, the Jeep engine will be able to return to running smoothly so maximum power and fuel efficiency can be achieved.