| The fuel pressure regulating valve -N276--2- is located in the fuel rail. It maintains a constant pressure in the fuel rail and the injector pipes (high-pressure fuel circuit). |
| If the pressure in the high-pressure fuel circuit is too high, the regulating valve opens to allow some of the fuel to flow back from the fuel rail to the fuel tank via a return line. |
| If the pressure in the high-pressure fuel circuit is too low, the fuel pressure regulating valve -N276- closes and seals off the high-pressure section of the system from the low-pressure section. |
Note | Fuel pressure regulating valve -N276- must always be renewed after it has been removed. |
WARNING | t
| Always observe rules for cleanliness and instructions for working on fuel system → Chapter. |
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| Follow these instructions and rules for cleanliness before starting work and while working on the fuel system. |
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| Before removal, clean area around thread for fuel pressure regulating valve -N276- using commercial cleaning solution or similar (no dirt must enter opening in fuel rail). |
Note | Clean carefully; cleaning solution must not enter the electrical connector. |
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| Dry off fuel pressure regulating valve -N276-. |
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| Slacken union nut (counterhold at hexagon flats on housing). Then unscrew and remove by hand. |
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| Extract dirt from opening in fuel rail (thread and sealing surface) using a vacuum cleaner. Do not use metal tools, etc. |
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| Seal off open fuel rail connection with clean plug. |
Note | t
| The fuel pressure regulating valve -N276- has a deformable sealing lip and no separate seal; it can therefore be used only once. |
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| Check that sealing surfaces (deformable sealing lip) and threads on new fuel pressure regulating valve -N276- are not damaged. |
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| Check sealing surface at opening in fuel rail. |
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| The beginning of the thread and the deformable sealing lip of the fuel pressure regulating valve -N276- must be coated with diesel fuel. |
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| Screw on union nut by hand. |
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| Align new regulating valve so that connecting wire is free of tension after connector is attached. |
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| Hold regulating valve in this position by holding hexagon flats on housing of regulating valve with open-end spanner or pliers (water pump pliers or similar). |
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| Use suitable torque wrench with an open-end spanner insert (30 mm) to tighten union nut. |
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| After installation, run engine at moderate speed for several minutes and then switch off. |
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| Check fuel system for leaks. |
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| Interrogate event memory. |
| After renewing high-pressure pump or fuel pressure regulating valve -N276-, learnt values must be re-adapted; see „Guided Functions“ in → Vehicle diagnostic tester |
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| After completing the repair, road-test the vehicle. Accelerate with full throttle at least once. Then check the high-pressure section of the fuel system again for leaks. |
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| Interrogate event memory again. |
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