Replace the failed Glow Plugs in your 1999-2003 Ford 7.3L Powerstroke. Symptoms of a faulty glow plug include a check engine light (CEL), hard starting, rough idle/misfire, loss of power, black or white smoke, and a decrease in fuel efficiency. A glow plug is a heating element that is used to heat incoming fuel and air. This is designed to help aid the combustion of fuel in a diesel engine especially during startup. This heat can be necessary for a diesel engine to start, run, and function optimally especially in cold weather conditions. Many diesel engines utilize one glow plug in each cylinder, either in the pre-chamber or in the combustion chamber. If one or more glow plugs fail, the combustion chamber won't have the necessary heat required to ignite the fuel. It may take several attempts at starting the vehicle before achieving ignition, depending on the outside temperature. In freezing winter temperatures, it is also possible for a diesel to not start without operational glow plugs. Shop glow plugs, harnesses, and controller/control modules from all the leading manufacturers such as Diesel RX, Dorman, Bostech, Ford/Motorcraft, Dtech, Alliant Power, GM/AC Delco, and Diamond Advantage By Navistar.