Mercedes Sprinter fuel pump and/or filter issues?????

Hello......my lwb 311 sprinter, had an oil cap malfunction, oil every where ect. Sorted it before it went dry, steam cleaned and toped back up.

Ran fine for one day,
Then the battery dies, replaced this, still woldnt turn over, replaced the fuel filter as the engine seemed to tbe starved. Now it will only turn over if i fill the filter with fuel and spray easy start in the air filter. Then i get the edc light and i can see air in the fuel line, it dies and wont turn over????

Could it be the pump? Dont know where to go from here.