Note: See the warnings provided in Section General information and precautions.
This procedure only relieves pressure in the fuel system. Fuel will remain in the system and components - be prepared to collect traces of spilled fuel.
1. The fuel system path consists of a fuel pump installed inside the fuel tank, a fuel filter, an injection injector, a throttle body with a built-in pressure regulator, as well as metal tubes and rubber hoses of the fuel supply and return lines. The cavities of all the listed components are filled with fuel, which is under pressure when the engine is running and/or the ignition is on. The pressure remains in the system for some time after the ignition is turned off and must be released before any work related to disconnecting the path or removing components. Ideally, servicing the system should only begin after the engine has completely cooled down.
2. Disconnect the negative cable from the battery.
3. Remove the fuel pump relay and/or fuse (see section Removal and installation components of the Bosch Mono-Motronic system).
4. After disconnecting the pump, temporarily connect the battery and turn the engine with the starter for about ten seconds. If the engine starts during cranking, wait until it stops spontaneously. During cranking, the injector should open as many times as necessary to completely release the residual pressure in the fuel system, which will prevent fuel from splashing when disconnecting the lines.
5. Remove the key from the ignition and disconnect the negative battery cable. You can now replace the fuel pump relay/fuse, provided that the battery remains disconnected and the ignition is not turned on until the work is completed.
Caution: Turning the ignition on while the fuel pump is energized may result in unexpected fuel spraying through the openings of the disconnected lines.
6. Place a suitable drain container under the nipple connection to be disconnected. Have a sufficient number of rags available to collect any spilled fuel.
7. Slowly loosen the clamp or union nut, wrap the joint with a rag. When the emission of residual fuel stops, completely disconnect the connector. Plug the open ends of the lines/nipples with plugs in order to minimize fuel loss and to avoid internal contamination of the fuel system.
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