The "spark" made by your spark plug is like a tiny bolt of lightning; it's that powerful. Each time it sparks, a wee bit of material is lost from the electrodes. Over the millions and millions of sparks that happen over the thousands of miles you drive, enough material is lost from the spark plug to affect its performance. That's one reason they need to be replaced. At Greenhaven Shell in Sacramento we install quality NAPA replacement parts. Give us a call at 916.422.6053 and let us help keep you safely and economically on the road.