Problems starting 2003 defender TD5 110

Hi there, I have had problems with starting the engine. From time to time I can't start the engine, it takes a few attempts to start and the amount of attempts seams to increase aport from this there is a very rare, short power loss for a few seconds and then it kicks back in. I have had the diesel lift pump replaced and there seems to have been some corrosion on the fuel pump relay which was cleaned and swapped out with the other ones and tested for functionality. The issue doesn't represent itself when checked out by an mechanic so they say they can't pin down what it could be. Is there anybody here with similar experiences and maybe some pointers where to start to investigate. Thanks for your help.

Welcome this Is not for the td5 but may give you a few pointers

Maybe a problem with the fuel pressure regulator?
Have you purged the fuel system to expell any air?

Thanks, heaps for this. It seems odd that the truck runs perfectly well for a while and just has the issues at random. Anyway, this will give me a few pointers to start invstigating.

Don't forget the ECU. I had a few of these symptoms. Sometimes the starter would churn impotently but the engine would not fire, and then when you tried it a little later up it started. Sometimes there would be a hesitation of a few seconds when you pressed the accelerator, for example when trying to overtake, and then it would pick up speed as normal. Eventually I was left stranded at the roadside one day when the engine cut out and it turned out to be an ECU problem. Though the Nanocom didn't show any faults that would be fatal, a garage's Autologic machine showed the dreaded 'topside switch failure'. Since having a new ECU, it hasn't shown any similar faults. So I suspect the ECU was responsible for the intermittent problems.