He has the SE variant 330d with exactly the same running gear as mine, i.e. same M57 engine.
The car had gradually developed a stuttering hesitation at high revs, specifically 3800rpm. In fact it simply wouldn't rev higher than 3800rpm.
We deduced it had to be not enough of something getting into the engine such that it couldn't rev up freely. So trim panels came off and we started investigating.
The video below shows what happened when you revved the car. Please ignore the sound change at the end of the video, despite it sounding like a turbo waste gate or pressure being released, for some reason my phone adjusted how it recorded.
The first things that came to mind as a potential cause were as follows;
- Vacuum hoses
- Injectors
- EGR clogged up
- MAF faulty/dirty
We started off with the easy ones to check. With a bit of perseverance the MAF was removed and cleaned with a spray specifically for the task. You can read further into this when I cleaned the MAF sensor on my car last year.
After leaving the sensor to dry thoroughly it was refitted and the engine tested again. No change. So to check if the MAF was faulty and not just dirty, we ran the engine again with it disconnected, still no change.
Next up was the EGR. Post removal I was quite shocked at how clean it was, compared to when I cleaned my EGR it was spotless. Nevertheless it got a good clean and was refitted, yet again the engine hesitated.
The last two on our list was a fair job to check, so I resorted to Google searching. Turns out it's a fairly common problem, and it seemed to be accountable to the mid car fuel pump. This would make sense with our "engine is not going enough of something" theory.
Dad decided he'd take the plunge and ordered a new diesel fuel pump from Eurocarparts, Pierburg branded.
Unfortunately I haven't got any images of the fitting process, but he tells me it wasn't much of a job really and only took him a couple of hours from getting the car on the ramps to a test drive.
I can also confirm that it was indeed this diesel fuel pump that was at fault. The engine is back to normal, revving freely up to the red line. Needless to say he was quite chuffed!