E250 W212 - OM651 - P0299 Turbo Underboost

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New Member
Nov 24, 2021
N. Ireland
Hi All,

2014 E250 CDi W212 with the OM651 engine - a few weeks ago car drove normal under light load but I had EML light on under hard acceleration and limp mode with following code -

P0087 - Fuel Rail/System Pressure - Too Low

Diagnosed as a faulty Fuel Quantity Valve (Y94) which I replaced. To get access I had to remove -

1. Vacuum Tank Reservoir
2. EGR Cooler
3. Exhaust Gas Re-circ pipe
4. Intake Air Duct
5. Throttle Body
6. MAP Boost Pressure Sensor

Built back up in reverse order - replacing anything which was removed, reinstalling plugs, hoses etc.

Started the car and took it for a test drive - no power and felt like limp mode. Initially no EML light on but after a couple of miles it did eventually come on with fault code -

P0299 Turbo Underboost

Could something have happened during replacement of the Y94 be causing this issue? Nothing, that I can see, was damaged or in poor condition and everything was refitted exactly as it was before the strip down.

Or is it more likely to be a separate issue?

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