TD4 fuelling issue

05 Td4 with 135k.

Sometimes it starts, idles slowly, then stalls, and takes a lot of cranking to get it going. Usually after being left either overnight or for a few hours. But other times, it starts just fine. LP pump can be heard running even when the car's playing up.

Either way, once running, it goes like a rocket and pulls well up hills, except...

Again intermittently, it doesn't seem to respond well at junctions - you try to pull away and it'll nearly stall.

No codes.

Jobs done:

1. New glow plugs (well, three. I sheared one off.)
2. Injectors were renewed before we bought it.
3. HP pump has been reconditioned, including regulator O-ring
4. Fuel rail sensor harness has been upgraded.
5. Wheelarch filter replaced with Mahle one.

Looks like the LP pump is the problem, but how come it pulls so well when going? Do you think at start-up and lower engine speeds (junctions) that the pump is getting a lower voltage and the problem surfaces? I've not seen this set of symptoms before in the many Td4 performance threads.

It could be the low pressure fuel pump, as quality ones or originals take a while to die and give intermittent issues.
But it does sound like fuel isn't being held in the pipes and is draining back. As you've done the HP o rings it might be worth checking everything is tight or hasn't come loose.
Mike

It's definitely worthwhile looking at the low and high pressure pumps live data. Sounds like a low pressure pump is failing to me. Low pressure must be over 320kpa or it'll have starting and running problems.

I'll scan and report back.