Air in Fuel filter 2.8GU

[Hippo]

Have been having problems with Cold starting my ’99 2.8 GU for a couple of months. Took advice from forum members and installed the advance plate for the injector pump, This worked well for a couple of weeks but now back to old ways. Have removed plate to check ‘O’ ring which seems to be fine. So she’s back to taking a good couple of minutes or so to start (lucky battery is new!). Good volts at bus bar
Have noticed that the primer pump on top of the fuel filter can be pumped 4-5 times before it becomes solid. Does this mean I’m getting air in the system and if so how do I bleed it out. Manual just says prime until firm which I have done on numerous occasions, but leave her overnight and i'm back to the start. Have to assume I’m getting air into system somewhere or is this normal? Can’t say I noticed what it was like prior to these problems.
Doesn’t seem to make a difference if I prime her before trying to start, still doesn’t like these cold mornings! But need to eliminate this as a cause. Once started, then no probs starting for next 5-6 hours,
Have already replaced Glow Plugs, battery fuel filter so have run out of ideas.
Any ideas regarding air in fuel system and the Cold start problem welcome

[the ferret]

Mate have you checked all hose fittings between the tank and the injector pump, also check that the fuel cap is not sealing creating a vacuum in the tank, re check the seal at the fuel filter and make sure all fittings on the primer are tight.
Your problem may even be the fuel cut off solenoid on the injector pump itself or a worn primer pump.
It wont matter how new the battery and glo plugs are, if you have air in the system, it will be hard to start.
Cheers, the ferret.