And after all that ...... it doesn't start

Well, it did start, briefly. Ran for about 5 seconds, revs tailed off and it died and now it won't restart. It fires one cylinder every now and then but that's about it. Immobiliser is wired as per pic above, ecu relay is fitted, fuel pump primes, every thing is plugged in, spare vacuum ports on throttle body are blanked off, only thing not plugged in is the lambda (struggling to fit the miltek decat - so much for buying quality so I didn't have to mess about with it

) but can't imagine this would have any effect.
Any ideas/obvious things I haven't thought of?
Cheers