Cant start - Fuel/air issues td5 110

Morning all, i have a 2004, td5 110.

A month or so ago i had a new rear cross member fitted/welded by the garage, which would have involved dropping the tank and undoing all the fuel connections to tank and pump.
I hadn't driven the Landy much at all for the last couple of weeks only short journeys and had started to suspect that the vehicle wasn't right and although would rev/accelerate fine, wouldn't really develop any power.
Fast forward to last week when i had to drive to a festival fully loaded with all the axe throwing and mobile range equipment 140 mile journey. Problems started straight away and got a worse, fast and shaky tick over, no umph or power when accelerating, very noisy/high pitch whine from the fuel pump area, then trouble starting if i stopped, it was the same all the way home.
I have a hole in the floor so yesterday i undid and redid the perfectly looking fuel pump connectors and did the fuel purge (position 2, 15 secs, pump accel 6 times), it started fractionally better but still poorly (its always great at starting usually). I also had a fuel filter delivered so popped that on, it did start and seem to tick over well, but got distracted by life and left the vehicle for a test drive till later. Now it wont start at all (even after three purge attempts) and i have flattened the battery. During the purge if the filter is held it feels like there is lots of bubbly air inside.
I am thinking there is a lot of air or an air lock somewhere?
Once i have charged the battery, where do i start.
The Landy has had a new vdo fuel pump 5 years ago, a new fuel filter assembly and a new fuel cooler after similar problems but has run faultlessly since. To confuse matters, i have a lot of oil in the engine bay and signs of a tiny traces at the ecu plug under the drivers seat, its currently very clean as i checked this and the MAF sensor during the journey.
lets start with the easy things please

To check for air coming through the system could you disconnect fuel pipe in the engine bay and run the pump with pipe in a clear jar to check.

Its a td5, is the fuel not at a high pressure in the engine bay?

As you had the tank removed for the cross member replacement have you checked the fuel delivery pump filter in the tank you may have disturbed sediment in the tank and it's starving the pump

If air is getting in it has to be at the pump, any thing after would show as a leak.

mystery said:

As you had the tank removed for the cross member replacement have you checked the fuel delivery pump filter in the tank you may have disturbed sediment in the tank and it's starving the pump

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Brilliant, I didnt know there was a filter in the tank/on the pump, do you have a photo or part number and can tell me where it is so i can check/clean

It's on the bottom of the pump in the plastic housing.
If you have oil in the ecu then change the injector wire loom.

Aaaaaaaaaargh, taken the pump out, cleaned the filter/housing, and all the fuel line connectors, and now i still cant start. Done three of the purge cycles too and flattened battery for the second time.

So its either an air lock that wont come out or fuel not arriving at the injectors because of a fuel pump issue.

As it was perfect before the cross member work and the fuel pump/fuel cooler/filter assembly have all been replaced in the past im at a loss.

Before i buy another new pump as the next step, is there anything i can try? doing a purge cycle and cracking open the bottom of the filter perhaps or something nearer to the injectors?

Fuel pressure gauge connected at the fuel pressure regulator?
Under a certain voltage it won't start, apparently.

Anaconda said:

Fuel pressure gauge connected at the fuel pressure regulator?
Under a certain voltage it won't start, apparently.

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worth a look thank you. Where do i find the fuel pressure guage and the fuel pressure regulator?

I’ve just had a similar issue with my D2, turned out it was the pump, mine had stood for a time with very little fuel in the tank, apparently this can cause the pump to seize as it sort of dries out ?