Right first things first, I use biodiesel.

I started her up this morning and it was smoking really bad but didnt think nothing of it as it was cold.. running like normal along the A63 then 10 minutes in, the speed drops to 50mph which I thought was strange but thought whatever and cracked on, then I noticed that it wad rummimg rough and the boost gauge was on 0, long story short pulled into Ferrybridge services and did all the usual checks, still smoking like hell and running really rough so thought **** this and turned around bsck home (40 miles) turbo was working again and running fine but crap at low speeds, pull up at a traffic light and all yiu can see is white smoke every where, exhaust is popping and crackling. After punching my steering wheel serveral times I made it home after buying a new fuel filter which had a new one 4 weeks ago,
parked up and left it otherwise I would of got the hammer out the boot.

replaced the fuel filter an hour ago and no joy, wont tick over no nothing, struggling. Loosened the nut on top of fuel filter housing and air is coming out.

Seriously no idea what to do now.

any advice would be appreciated.

sucking in air somwhere?

its not instant, but replacing the pipe between the filter and the ip with some clear pipe will allow you to see if any air has ingressed.

bio eats (some) seals, but there's nothing that should have gone before the lift pump - apart from, maybe, the seal in the sedimenter

the ip front seal goes with bio, but that will cause fuel into the timing belt housing, rather than air ingress

really, i suspect, a bit of clear nylon pipe between the filter and the IP will be your first call.

(i too run on bio)

ahh - i missed your line about air comming out of the filter top - that's it then.

my disco is a 300, but there's only a few places to look -

the bends on the top of the tank sender unit (under the hatch in the boot on the 300) - id say unlikley if youve not messed with them recently
the sedimenter (chassis mounted)
the lift pump - theyre cheap - £23 or so delivered for an OEM - the OEMs have a seal in the flying saucer bit too - just an o-ring

the lines might have failed, but id put my money on the lift pump, with a backup bet on the sedimenter - post lift pump, youll get leaks, rather than air ingress, as the pressure will be above atmospheric rather than below.

Timing jumped a couple of tooth, there was oil in the timing housing so hopefully it is just the crank seal as no oil anywhere else, will find out more tomorrow when it's stripped etc

Lift pump. It's always the lift pump. I hate sodding lift pumps.

Sorted it last sunday just forgot to comment.

I left my wading plug it, so when the front inner crank oil seal went. The oil had nowhere to go except up into the timing housing and caused it to jump 3 teeth so after putting new seal in and replacing the knsckered pulley and replacing cam belt snd did timing, it runs like a dream.