You can help narrow down your problem by checking a couple of areas. First, do you have severe blow by if you remove the oil
filler cap on top of the engine
. That will be a sure sign pressure is seeping past the rings to the sump.
Try cracking the pipe to the each injector and allowing the fuel to bleed. This causes the injector to not biuld enough pressure and won't fire in the fuel dose. If the cylinder has been firing, it will drop out and you will notice the engine
will run (at idle) a little ruffer. The cylinder that is not firing at all will make no change when you crack the injector fuel line. That will at least narrow down what cylinder/s is causing the issue. Then you can check the injector and valve clearance. Tappet clearance can be an easy mistake.
If you suspect and injector, swap over another cylinders and see if the miss now swaps too.
Apart from that, you will have to run a compression
test and see what the pressures are. A leakdown test may help pinpoint where the pressure is going. You will hear the escaping air going to the place of suspect.
White smoke is a sign that the cylinder is not firing but fuel is entering. So a bleeding problem should not be the issue. One of the worst case scenarios is that the head gasket
has not sealed or damaged and you are getting water in a cylinder. It doesn't take much to stop the cylinder from firing. But normally shows it's ugly head when you go to turn the engine over a few days later and it locks solid.
That should give you some starters anyway.