Abstract: An electronically controlled diesel engine for a vehicle which may act as an air compressor in addition to acting as a power source for the vehicle. When acting in the air compressor function, one end cylinder is converted to the function to provide compressed air to air tanks on the vehicle. The air from this combination compressor and power cylinder may be used to fill air tanks which provide air for braking in vehicles such as heavy trucks. The combination compressor and power cylinder has an exhaust isolation valve in the exhaust manifold to isolate an air collection area and a relief/check valve engaged on an upstream side to the air collection area and to an air tank in the air system for the vehicle on the downstream side. An electronic controller means controls the fuel injector for the combination compressor and power cylinder and the exhaust isolation valve. Various types of diesel engines may be modified to become an electronic engine-air compressor system in accordance with this invention.