| Fuel pressure regulating valve -N276--arrow- is located in the high-pressure reservoir. It maintains constant pressure in the high-pressure reservoir and injection lines (fuel high-pressure 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 from the high-pressure reservoir 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 | The fuel pressure regulating valve -N276- cannot be re-used. |
Caution | Risk of malfunctions caused by dirt. |
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| Remove the high pressure reservoir (rail element) → Chapter. |
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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 solvent 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 hexagonal 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 opening in fuel rail with a clean plug. |
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| 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 the connecting line 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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| Install the high pressure reservoir (rail element) → Chapter. |
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| Let the engine run for a few minutes at average speed after the assembly and then turn it off again. |
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| Ensure that the fuel system is completely sealed. |
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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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