an injector cleaner, but also use Power Services supplement on a regular basis (at least every other tank in a boat engine that may see prolonged periods at idle). The Lucas cleaner works well every third or forth tank for us. These are not that expensive in the quantities used in most boats. The company I work for and my brother-in-law's trucking company are convinced these additives add many thousands of miles to both the injectors and injection pumps in their trucks and heavy equipment (which make up about half of all diesel engine service problems). Some are not convinced, but I have seen enough of these engines torn down to believe they work. ...imho.