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Removing and installing fuel pressure senderG247 > < Checking fuel pressure regulating valveN276

A5

Removing and installing fuel pressure regulating valveN276
Removing and installing fuel pressure regulating valve -N276-
  Note
t  The fuel pressure regulating valve -N276- maintains a constant pressure in the fuel rail and the injector pipes (high-pressure fuel circuit).
t  It is not possible to start engine if fuel pressure regulating valve -N276- is defective.
t  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 hose.
t  If the pressure in the high-pressure fuel circuit is too low, the valve closes and seals off the high-pressure section of the system from the low-pressure section.
t  The fuel pressure regulating valve -N276- has a deformable sealing lip and can only be used once. Do not install it for test purposes.
Removing
–  Pull off engine cover panel → Chapter.
  WARNING
Risk of malfunctions caused by dirt.
Observe → Chapter.
–  Clean thread and area all around fuel pressure regulating valve with engine cleaner or brake cleaner and dry.
  Note
t  Clean carefully; cleaning solution must not enter the electrical connector.
t  Make sure no dirt gets into opening in fuel rail.
–  Remove banjo bolt for fuel return hoses.
   
–  Unplug electrical connector -arrow- at fuel pressure regulating valve -N276-.
–  Loosen union nut at regulating valve (counterhold at fuel rail). Then remove by hand.
–  Remove dirt from thread and sealing surface of fuel rail using a vacuum cleaner. Do not use metal tools, etc.
  Note
Seal off opening in fuel rail immediately with a suitable plug to prevent dirt from entering.
Installing
Installation is carried out in the reverse order; note the following:
  Note
t  The fuel pressure regulating valve -N276- has a deformable sealing lip and no separate seal; it can therefore be used only once.
t  Check that deformable sealing lip and thread on new fuel pressure regulating valve -N276- are not damaged.
t  Check sealing surface at opening in fuel rail.
t  The beginning of the thread and the deformable sealing lip of the fuel pressure regulating valve -N276- must be coated with diesel fuel.
  A23-10534
–  Position fuel pressure regulating valve -N276- so that electrical wiring is not under tension when connector -arrow- is plugged in.
–  Tighten union nut on regulating valve in 4 stages (counterhold hexagon flats on housing):
l  Tightening torque → Fig..
–  Tighten banjo bolt for fuel return lines with new seals to 25 Nm.
Bleeding fuel system and checking for leaks
–  After installation, run engine at moderate speed for several minutes and then switch off.
  Note
The fuel system is „self-bleeding“; do NOT open the high-pressure connections.
–  Interrogate event memory and erase it if necessary.
–  Switch off ignition.
–  Carefully check the entire fuel system for leaks.
Renew affected component if leakage still occurs after tightening to correct torque.
After renewing high-pressure pump and/or fuel pressure regulating valve -N276-, adaption must be performed. Use → Vehicle diagnostic tester.
–  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.
  Note
If there is any air left in the fuel system, the engine may switch to the backup mode ('emergency running' mode) during the road test. Switch off the engine and erase the event memory. Then continue the road test.
–  After road test, interrogate event memory again.
  A23-10534

Removing and installing fuel pressure senderG247 > < Checking fuel pressure regulating valveN276