Besides the actual fuel that goes into it, the Dodge spark plug differentiates a gasoline engine from a diesel one. Yes there are other differences but if you see an engine with spark plugs you know the fuel that it uses automatically. The spark plug is the electrical component on your engine that initiates the explosion in the combustion chamber. The spark it generates has to be in the correct heat range, at the right depth and gap of the plug must also conform to the specifications of the engine. Each Dodge engine has one spark plug per cylinder. They must be kept in proper working order or your engine will not be able to perform at its peak efficiency level. This is why they are changed out every 12,000 to 24,000 miles. At 12,000 miles you may be able to just clean your plugs. A faulty plug will cause an engine to run rough or uneven. To test the Dodge spark plug it must first be pulled from the engine then reconnected to the spark wire. With the engine turning over and the plug grounded to the engine, the spark at the electrode must be observed. This should be easy to see. If you need to do this test in a dark garage to see the spark, then it is weak and replacement is recommended. When replacing the spark plugs on your Dodge, handle them with care. The ceramic chamber in them is very delicate. If the plug is dropped for any reason it should be discarded and another put in its place. The reasoning behind this is that a hairline crack could be in the dropped plug. This will cause a leak in the vacuum section of the plug causing it to be faulty and not produce a spark. With a new set of plugs in your Dodge the performance and mileage will be at their maximum level.