Help I'm at my witts end

I've got a 300tdi 1994 Disco manual.
The issue is it starts n revs, it'll drive for a couple of hundred yards, then losses all power.
I've up to now changed the filter, fuel line, lift pump (be it a cheep one as all they had) and even drilled the top the sender to put a new pipe in.
After changing all this it drove great for around 20 mile then it started again. When its nearly cut out as if its got no fuel I've turned it off n tried unscrewing the water drain on the filter and it sucks a load of air in as if its under vacuum. I've drained the tank too and put fresh derv in and also checked the tank cap.
TIA Steve.

check the pick up pipe in the tank,had the same happen on a defender, turned out to be a piece of insulation tape in the tank getting sucked onto the end of the pipe

I've had it all off again n its all clear. I emptied the tank from the hole where the sender goes n looked around inside with a light n theres nothing to be seen.

Bit of a guess as not sure about disco's but is it possible to get the pipes the wrong way round on the lift pump? FIP could be running on fuel in the filter until it runs out or lift pump causes sufficient suction to stop FIP sucking fuel from filter? Also tried running without fuel cap (or cheap temp onefitted) in case vent not working?

Just to clarify - have you tried with direct feed with pipe from a jerry can ?

Yer I tried direct feed before the new pump was fitted n it reved fine. The pipes cant be wrong way because I know which is the new pipe plus I've bled it up a few times n if it was the wrong way it wouldn't I'd of thought. I've had the cap off plus I had the fuel sender out n drilled a new stand pipe in case it sucking air in though the sender so its not air tight no longer. The pipe I've put in I've curled over at the end so its not directly on the bottom too.

Tried a piece of clear pipe to see if any air is being drawn in ?

Leak-offs ? ermmm...

you need to be sure lift pump is pulling fuel through with no air byu removing outlet pipe ,injection pump itself will pull fuel through as long as system has no leaks , clear pipe between injection pump and filter helps to see if air is been sucked in ,check front banjo on injection pump has big hole and banjo on rear has tiny ,presume youve bypassed sedimentor

Funny enough I've put a cheap clear filter in too just so theres something before the lift pump n nothing can be seen.
Thanks guys for the tips keep them coming, I'm thinking it may be the cheap lift pump giving up after the 20miles.

Be wary of cheap clear filters (or even clear expensive filters for that matter). those filters are made for petrol and clog up with diesel (don't ask me how I know).

I took that filter back off n all is well again besides the float sender isn't working now. :-( Thanks guys

One step forward

Just to re-cap about how I know that those cheapo in-line filters are meant for petrol. I nearly got stranded at sea a couple of years ago thanks to one of those filters!