Fuel pressure.....stalling

Morning all,
Weird problem on the TD5, so it was running good, but the diesel heater we have wasn't getting a good enough fuel supply as I had temporarily tucked the fuel line under one of the filler joins and clamped up with jubilee clip......as the tube got squashed it lost supply so the only changes recently I've done are......

• Service, so new fuel filter which obviously needed priming via throttle pedal
• Put a standpipe in the tank which has a bloody great seal on it and seems fine.....
• I had drilled a hole in the filler neck (using a TDI filler and fuel cap) and was running a standpipe down the filler neck which didn't work for some reason and I didn't like it so I removed it and blanked the hole with a CSK M6 bolt, washer, nut...

So driving yesterday, after about 45 mins, no power, ended up on hard shoulder priming it and eventually drove off.

45 mins later, same again, and this morning same again.

So first off I was running the diesel heater while driving, it uses a teeny amount of diesel but could that be releasing pressure from fuel tank and causing issues? Or could it be the bolt in the filler neck? I thought the lines were pressurised but is the tank?

Thanks in advance guys

teensy update.......seems to be worse when the tank has less diesel in it....quarter of a tank today vs 3/4 the other day and it's way worse.

Could be pump playing up, or air leak by filter.

Thank you MJI
Pump sounds like it's running fine, was actually replaced quite recently.

Is there any way at all it could be the fuel filter itself? I normally use Mahle and only had a Britpart one.....but surely it's only a filter!?

What about the non return valve or bleed valve in the filter block?

Filter heads can go porous.

Does it run ok with a full tank.?

May need to ask in discovery section.

Thank you! It's on a td5 defender 130 actually although I know it's all the same with the Discovery 2 hence I stuck it in this section but yeah I guess it's more a vehicle thing than an engine thing!

I have some time today, I have a new non return valve and bleed valve for the filter block so fingers crossed something decides to work