To check for swarf in the high-pressure pump the valve for fuel metering N290 (IMV), contrary to the repair manual, may be removed.
When removing the valve for fuel metering N290 observe the following points:
When removing the fuel metering valve the high pressure pump can also damaged by dirt from outside.
• Before removing the N290 carefully and thoroughly clean the surrounding area.
• If there is no swarf on the N290 or in the hole, refit the valve straight away. Check both O rings. If they are damaged, replace the high pressure pump.
• When fitting the N290 apply fuel or oil on the lower O ring.
• Push in the N290 by turning it slightly.
• Tighten both M5 bolts by hand - do not lubricate the thread.
• Pre-tighten with 2 Nm and then to 6.5 – 7 Nm.
If there is a swarf accumulation, the complete high pressure fuel system must be replaced:
- Replace high pressure pump, pressure control valve, rail, injectors with high-pressure pipes, fuel pressure sender and overflow oil pipe with bleeder valve
In the low pressure fuel system the fuel pump in the tank, the fuel filter and the electric fuel pump must be replaced.
Clean or flush out fuel tank and fuel supply and return pipes (low pressure) between high pressure pump/rail and tank. A replacement is not necessary.
- Suck out the tank before changing the fuel pump and flush out the fuel pipes.
- After removing the fuel pump wipe the tank floor as far as possible with a fluff-free cloth.
BUT
From experience I have found the IMV is often the fault on these, the valve is not available separately from VW - a new H.P pump is required,
I believe these are available separately from some diesel specialists now.
Check the ability of the low pressure side to maintain it's specified pressure - 4.5 Bar is the specified value, you may see it flicking up to 6 bar at idle. Raising the idle speed will even the fluctuations out & give you a steady reading at the specified 4.5 bar if the low pressure side is okay,
Scope the rail pressure sensor - if the IMV is sticking due to swarf or a failing IMV valve you should see the rail pressure bouncing as it tries to control the pressure in the rail against the IMV issues.
I notice you are using VCDS, on the dealer tool there is a basic setting that resets the high pressure regulation & can provide a temporary fix to the poor running if the HP pump is starting to fail - It may be worth a look to see if VCDS can base set this system?
Milan