A possible culprit for the car not starting is the water temperature sensor that goes into the back of the head, it's a pig to get to but I had starting problems with my 4x4 Sapphire once and it was the wts that was gone/faulty

Also what does the car do when you are out driving it and it comes on boost? Have you got like a mis-fire problem and what is the rev counter doing when you are giving the car a bit of boost?