The invention provides compositions and methods for more thoroughly cleaning internal combustion engines, fuel systems and emission systems and that operate with reduced toxic emissions. The invention provides an apparatus that contains at least one vessel for receiving a cleaning fluid and an electrode in a cleaning fluid flow path configured to apply a charge to a cleaning fluid. The cleaning fluids are unique fuel derived products which do not contain detergents. The apparatus is unique in that it can provide any of several cleaning processes including a pre-combustion cleaning process, a post-combustion cleaning process or a combined pre-combustion and post-combustion cleaning process. The method is particularly effective at cleaning oxygen sensors in exhaust systems.