Major headscratcher, hdi not starting.

[shorta]

So, first post on here, I've been lurking for years, but I'm absolutely stuck now, and I could use some input. I've got an X reg hdi, 3 plug ECU, pro Steve stage one remap. It was running fine for the last 2 years and 50k, or thereabouts, but recently it started cutting out. Lift pump runs, and primes the system, and most times after its cut out I've been able to prime it a few times and get it to restart. It's also been noticeably harder to start. I've tried cleaning out the fuel pressure regulator with brake cleaner and wd40, and it would start absolutely fine the first time after refitting, and then go back to its usual self. Then last Wednesday it cut out and wouldn't restart. I wound up getting it recovered to work, going home and leaving it for a couple of days and when I came back to it, it started fine. Went round everything, replacing the fuel pressure regulator and fuel pressure sensor with ones from another car that ran fine, stripping the lift pump out to make sure the strainer was clear and drove 35 miles home without cutting out once. Drove to work the next morning and it cut out twice. Drove home that night and it cut out and wouldn't restart at all. Replaced the high pressure pump and injectors with ones bought off eBay, I don't know for a fact they're good but they were certainly advertised as such. Everything's reinstalled now and the car will not start at all, still. Plenty of fuel in the tank, lift pump runs and primes the system, testing with a multimeter shows 12v at the fuel pressure regulator plug when ignition is switched on, dropping to 7v while cranking, and recovering very very slowly afterwards. Sensor plug shows if I remember rightly 4.5v on the green wire, 9.5 on the white, and about 1v on the pink. There's no fuel coming out of the hp pump when cranking. I don't have access to pp2000 or anything to check fuel pressure or anything like that. 
Anybody got any ideas? I'm honestly at the end of my Tether, I can't afford to keep throwing parts at this, and if I can't cure it soon it's going to go for scrap.
Forgot to say, when cutting out, the only fault code showing was p0230. Which doesn't really narrow things down.
Tia guys