A4 1.9tdi 130 starts up facing down hill but on a flat no go :(

[icebreaker]

Hi everyone ,
I am having problems with my 1.9tdi a4 avant sport 145k
The engine turns over a few times then eventually fires up , i have tested the glow plugs and all four were dead so i have replaced them but the fault still persists . Tested the pump in tank all ok . Even when warm it struggles then fires up?

Could anybody help with this problem ?

Thanks

[adamss24]

Most likely worn tandem pump or air getting into the fuel system hence the hard starts...the fuel gets back to the tank when pointed uphill...