hi. as far as i am aware the 19j turbo diesel does not have a relay that keeps the plugs on. it operates straight from the ignition key and its down to the driver how long it is on for. I've recently changed our glow plugs as i was holding them on for 10 seconds and it still struggled to start and i randomly got smoke from behind the dash. The new plugs take 5 seconds and it fires up straight away.
Trickydicky, did you manage to sort your white smoking on start up? I've changed my injectors for genuine ones and all is sorted now.
charlie.