The fuel injection system delivers fuel or a fuel air mixture to the cylinders by means of pressure from a pump All diesel engine based automotive vehicles must use fuel injection by design because of diesels greater viscosity and the need to overcome the high pressure of the compressed air in the cylinders Gasoline engines can use either a carburettor or a fuel injection Over a period fuel injection has become the primary fuel delivery system in automotive gasoline engines by replacing the carburetor In gasoline engines the fuel usually is injected into the intake manifold and mixed with air and the resulting mixture is delivered to the cylinder