[bbowden]

09, 335d, 55k. Having very similar issues as welly. Rail actual drops below request enough to go into limp mode at WOT(forget the difference required for fault). Trying to read the rail pressure with an o scope I get the following. Does this point to the HPFP? Have testO logs as well, I’ll upload to link below shortly.https://drive.google.com/drive/folde...L4?usp=sharing

https://drive.google.com/drive/folders/1mhlO5oE_uNSDo0avyllN0DsKAH6JxhL4?usp=sharing

[welly]

Thought I would (finally) come back and wrap this one up with the resolution - nothing worse than someone who doesn't do this!!

Whilst chasing this (spectacularly unhelpful) fault code down, I changed the lift pump in the tank for a working second hand unit, the HPFP for an R90, fuel filter, fuel heater, did a leak back test, changed both rail sensors, and the rail itself, did a continuity test on the wiring, changed the quantity control valve, changed the EKPS ECU, had the previous map flashed back onto the car.

None of these made a dot of difference, and I was still suffering fuel pressure deviation.

Relying on pure old fashioned gut based on the logs looking like fuel supply starvation, I changed out the in tank pump again for a brand new unit. This then solved the problem.

I made a lot more work for myself by going with instinct in the first place, but using unknown second hand parts to try and diagnose... and a s**t load more money and time obviously.

So, for those looking for a possible fix for this kind of fault on the same motor in the future, I hope this thread may be useful!

[Asonchadwick]

By the way, as a bandaid maybe, if you have xhp you can reduce the power request in the software. I did this, it works. Keep reducing until you find the limits of the issue. Maybe also this will help with logging. You can reduce power all the way down to hardly anything and floor it and the car has no power lol.

[sergio 61]

Originally Posted by welly

I changed out the in tank pump again for a brand new unit. This then solved the problem.
!

I'm sorry, what is it that you changed out exactly? I'm having this low fuel pressure problem, where if I push the car a bit it gives engine malfunction reduced power. The car runs bad and has low power. This issue appeared (maybe coincidence?) when I put a bad diesel inside with some water. Now have emptied the whole tank, changed the fuel filter but the problem wasn't fixed.

[Asonchadwick]

Sounded like he replaced the lpfp