My glow plugs were not working when I got mine and I only found out on the first cold morning and it smoked and didn't want to start. Turned out to be that they had been over tightened and the insulator under the rail (the steel bar that connects all 4) had been squashed and 2 of the 4 plugs were shorting. It is easy to check the fuse to eliminate this, but if it starts straight up then dies I would say air leak.
