It may be required to replace the nozzles in the presence of the following symptoms: rough engine operation, reduced power and poor acceleration, engine starting problems, engine failure at idle speed, sharp noises at the start, increased CO content in the exhaust gases, malfunctioning oxygen level sensor, increased fuel consumption. The nozzle replacement procedure involves turning off the power supply of the car, releasing the pressure in the fuel system, draining the excess, disconnecting the junction block, disassembling the fuel line, removing the intake manifold, removing the nozzle rail, dismantling the nozzle and releasing the sealing rings on the replaced nozzle. Once these operations are completed, the nozzles are replaced.