Note. See the warnings in Section General information and precautions.
During this procedure, only pressure is released in the power system. At the same time, fuel remains in the path and components - get ready to collect traces of spilled fuel.
1. The power system path consists of a fuel pump installed inside the fuel tank, a fuel filter, an injection injector, a throttle body with a pressure regulator built into it, as well as metal tubes and rubber hoses for the fuel supply and return lines. The cavities of all listed components are filled with fuel, which is under pressure when the engine is running and / or the ignition is on. Pressure continues to be present in the system for some time after the ignition is turned off and must be relieved before starting any work related to disconnecting the tract or removing components. Ideally, maintenance of the system should be started only after the engine has completely cooled down.
2. Disconnect the negative cable from the battery.
3. Remove relay and/or fuel pump fuse (see Section Removal and installation of components of the Bosch Mono-Motronic system).
4. With the pump off, temporarily connect the battery and crank the engine with the starter for about ten seconds. If the engine starts while cranking, wait for it to stop spontaneously. The injector, during the cranking of the engine, should open as many times as necessary to completely relieve the residual pressure in the power system, which will avoid splashing fuel when the tract lines are disconnected.
5. Remove the key from the ignition and disconnect the negative cable from the battery. The fuel pump relay/fuse can now be replaced, provided that the battery remains disconnected and the ignition is not turned on until the work is completed.
Attention! Turning the ignition on while the fuel pump is energized can cause unexpected fuel spray through the openings of the disconnected lines.
6. Place a suitable drain container under the union to be removed. Prepare enough rags to catch spilled fuel.
7. Slowly loosen the clamp or union nut, wrap the joint with a rag. When the ejection of residual fuel stops, finally disconnect the connector. Plug open ends of lines/fittings with plugs to minimize fuel loss and avoid internal contamination of the fuel system.